Inheritance of Characteristics in Domestic Fowl

by Charles Benedict Davenport

C. RESULTS OF HYBRIDIZATION.

We have next to consider the nature of the inheritance when one parent belongs to an unbooted race, the other to a booted one (table 33).

Table 33.—Distribution of boot-grades in the F₁ generation of booted × non-booted parents.

A. COCHIN CROSSES.
Pen No.	Mother.				Father.				Grade of boot in offspring.
	No.	Gen.	Races.	Gra.	No.	Gen.	Races.	Gra.	0	1	2	3	4	5	6	7	8	9	10	Aver- age.
773	1334	P	W. Legh.	0	836	P	Bl. Coch.	10	...	...	...	3	1	1	1	1	...	2	...	5.44
773	193	P	Do.	0	836	P	Do.	10	...	1	2	6	8	7	4	2	...	...	...	4.27
773	1366	P	Do.	0	836	P	Do.	10	...	...	...	2	5	2	1	...	...	...	...	4.20
773	127	P	Do.	0	836	P	Do.	10	...	...	3	10	9	12	4	...	...	...	...	4.11
773	692	P	W. Legh. (R)	0	836	P	Do.	10	...	...	...	10	3	2	...	...	...	...	...	3.47
774	2075	P	Coch.	8	1431	P	W. Legh. (R)	0	6	1	1	...	1	...	...	...	...	...	...	0.78
Totals (111)									6	2	6	31	27	24	10	3	0	2	0	3.91
B. DARK BRAHMA CROSSES.
727	Y	P	D. Br.	10	381	P	Houd.	0	...	...	...	...	2	3	2	1	2	...	...	5.80
727	121	P	Do.	10	381	P	Do.	0	1	...	...	1	1	5	4	...	...	...	...	4.67
823	2030	P	Do.	7	3858	P	M × P	0	...	...	5	16	15	4	1	2	...	...	...	3.67
823	Y	P	Do.	8	3858	P	Do.	0	...	...	1	7	6	2	...	...	...	...	...	3.56
838	3814	P	W. Legh.	0	122	P	D. Br.	6	...	2	2	6	6	1	1	...	...	...	...	3.28
838	202	P	Min.	0	122	P	Do.	6	...	...	2	5	3	...	...	...	...	...	...	3.10
838	71	P	W. Legh.	0	122	P	Do.	6	...	...	...	1	...	...	...	...	...	...	...	3.00
838	3832	P	Do.	0	122	P	Do.	6	1	1	...	1	1	2...	...	...	...	...	...	3.00
838	10	P	Do.	0	122	P	Do.	6	...	1	...	3	1	...	...	...	...	...	...	2.80
816	121	P	D. Br.	9	4912	P	M × P	0	...	...	8	4	1	1	...	...	...	...	...	2.64
816	5838	P	Do.	9	4912	P	Do.	0	...	...	5	5	1	...	...	...	...	...	...	2.64
838	5418	P	W. L., Min.	0	122	P	D. Br.	6	1	1	3	3	1	1	...	...	...	...	...	2.50
816	5979	P	D. Br.	6	4912	P	M × P	0	4	3	4	7	4	1	1	...	...	...	...	2.46
816	2353	P	Do.	5	4912	P	Do.	0	...	2	2	4	1	...	...	...	...	...	...	2.44
816	5977	P	Do.	4	4912	P	Do.	0	...	3	2	1	...	1	...	...	...	...	...	2.14
816	5835	P	Do.	5	4912	P	Do.	0	3	5	5	8	3	...	...	...	...	...	...	2.12
816	5840	P	Do.	5	4912	P	Do.	0	5	1	3	4	1	...	...	...	...	...	...	1.64
823	6626	P	Do.	2	3858	P	Do.	0	1	10	2	2	...	...	...	...	...	...	...	1.33
816	5980	P	Do.	5	4912	P	Do.	0	5	8	1	5	...	...	...	...	...	...	...	1.32
Totals (268)									21	37	45	83	47	21	9	3	2	0	0	2.84
C. SILKIE CROSSES.
774	777	P	Silkie.	8	1176	P	W. Legh.	0	3	...	1	1	1	...	...	...	...	...	...	1.50
744	681	P	Do.	5	1176	P	Do.	0	11	2	1	1	1	1	...	...	...	...	...	0.94
744	469	P	Do.	1	1176	P	Do.	0	11	3	...	...	...	...	...	...	...	...	...	0.21
Totals (37)									25	5	2	2	2	1	0	0	0	0	0	0.76
SUMMARY.
Crosses.									Grades of boot in offspring, reduced to percentages.
									0	1	2	3	4	5	6	7	8	9	10	Aver- age.
Cochin.									5.4	1.8	5.4	28.0	24.3	21.6	9.0	2.7	0.0	1.8	...	3.91
Brahma.									7.8	13.8	16.8	31.0	17.5	7.8	3.4	1.1	0.7	...	...	2.84
Silkie.									67.6	13.5	5.4	5.4	5.4	2.7	...	...	...	...	...	0.76

An inspection of Table 33, which gives the distribution of grades of boot in the offspring constituting the first hybrid generation, might well lead to the conclusion that inheritance is here of a blending nature, or that, if either condition is dominant, it is the booted one, as suggested in my report of 1906. On this hypothesis the offspring with no boot illustrate imperfection of dominance, and one would say that, in booting, dominance is very imperfect.

However plausible such an interpretation might appear when based on the first hybrid generation alone, it becomes untenable when subsequent generations are taken into account, as we shall see later. The hypothesis breaks down completely in the second hybrid generation and we are forced to the opposite hypothesis, namely, that the clean-shanked condition is dominant. Such an hypothesis would seem, at first, to contravene the principle enunciated in my report of 1906 that the more progressive condition is dominant over the less progressive condition, or absence. But such is not necessarily the fact. We have no right to assume that presence of boot is the new character. The rest of the body of poultry (save the head) is covered with feathers. If the foot is not it must be because there is something in the skin of the foot that inhibits the development of feathers there. And this inhibiting factor is dominant over its absence.

Table 33 shows that the Silkie crosses yield an exceptionally high per cent of the dominant clear-footed condition. This is additional evidence that the Silkies are DR, and so this cross produces 50 per cent of pure extracted dominants in addition to 50 per cent of heterozygotes in booting.

To get further light on the nature of inheritance of booting we pass to the examination of the second hybrid generation (table 34).

In the case of Silkies, which throw 67.6 per cent clean-shanked progeny in F₁, we find in F₂ only about 60 per cent clean-shanked. This diminution is, of course, due to the extraction of some pure booted recessives, which draw from the proportion of clean shanks.

In the case of the Cochins and Dark Brahmas, expectation, with perfect dominance, is that 75 per cent of the offspring shall be clean-shanked. Since dominance is imperfect (as shown by the occurrence of many booted birds in F₁) we should look for an actual failure to reach so large a proportion, but we are hardly prepared for the result that in most of the F₂ crosses of Cochins and Brahmas less than 25 per cent of the offspring are clean-shanked. In 4 pens the average is only 10 to 12 per cent, and in one only 2 per cent of the offspring fail to develop feathers on the feet. What shall we say of such a case as the last? The history of the father (No. 666) is absolutely certain; his mother was No. 121, the original Dark Brahma female, with a boot of grade 9 and a record in her immediate progeny that indicates perfect purity of booting in her germ-cells. His father was a White Leghorn with clean shanks and without a suspicion of having such antipodal blood as the Asiatic in his ancestry. No. 666 is certainly heterozygous in boot, if boot is a single unit. The hens with which No. 666 were mated were clearly heterozygous, as is known not only from their ancestry, but also from their behavior when mated with another cock, No. 254, in which case they threw 12 per cent non-booted offspring. If now both parents are heterozygous they must produce 25 per cent recessives. This is the fact that forces us to conclude that clean shank is not recessive, but dominant and due to an inhibitor that frequently fails to dominate. In table 31 the two recessive varieties, mated inter se, produce no featherless shanks; the feathers grow freely as they do over the rest of the body. Some of the Silkies of table 31, however, are really heterozygous, with the dominant inhibitor not showing; consequently they throw a large proportion of non-booted offspring. In F₁, as table 33 shows, the heterozygous offspring have a reduced boot and perfect dominance—complete inhibition of boot—in from 6 to 68 per cent. Dominance is most complete in the Silkies, where, the feathering being feeble, the inhibitor has, as it were, less to do in overcoming it. In F₂ the expected 75 per cent dominant is approached in the case of the Silkies (62 per cent and 59 per cent, respectively), but inhibition is very imperfect in the Cochin and Brahma crosses, being reduced to between 25 and 2 per cent. More proof that boot is due to the absence of a factor rather than to its presence is found in this generation. If absence of boot is recessive, then, combined with imperfection of dominance, at least 25 per cent of the offspring should be recessive and probably a much larger proportion. The results in table 34 are absolutely incompatible with this hypothesis, since, in one case, there are only 2 per cent that can not develop boot. Two extracted clean-footed birds sometimes throw boot and sometimes not, and this result is to be expected on the hypothesis that clean-footedness is dominant, but two heavily booted birds can not transmit the boot inhibitor.

Table 34.—Distribution of boot-grade in the F₂ generation of booted × non-booted poultry.

COCHIN CROSSES.
Pen No.	Mother.				Father.				Offspring.
	No.	Gen.	Races.	Grade.	No.	Gen.	Races.	Grade.	Boot present.	Boot slight.	Boot absent.	P. ct. absent.
650	170	F1	Bl. Coch. × Wh. Legh	Pr.	265	F1	Bl. Coch. × Wh. Legh.	Pr.	19	2	2	8.7
650	263	F1	Do.	Pr.	265	F1	Do.	Pr.	36	2	2	5.0
650	278	F1	Do.	Pr.	265	F1	Do.	Pr.	26	4	4	11.8
650	361	F1	Do.	Pr.	265	F1	Do.	Pr.	24	2	9	25.7
650	364	F1	Do.	Pr.	265	F1	Do.	Pr.	39	5	3	6.4
			Totals (179)						144	15	20	11.1
654	602	F1	Wh. Legh. × Bf. Coch	Pr.	704	F1	Wh. Legh. × Bf. Coch	Pr.	11	4	5	25.0
654	828	F1	Do.	Pr.	704	F1	Do.	Pr.	7	11	0	0.0
654	640	F1	Do.	Pr.	704	F1	Do.	Pr.	13	2	3	16.7
654	696	F1	Do.	Pr.	704	F1	Do.	Pr.	8	5	8	38.1
654	767	F1	Do.	Pr.	704	F1	Do.	Pr.	3	1	3	42.9
654	697	F1	Do.	Pr.	704	F1	Do.	Pr.	4	3	6	46.2
			Totals (97)						46	26	25	25.8

TABLE 34.—Distribution of boot-grade in the F₂ generation of booted × non-booted poultry—Continued.

DARK BRAHMA CROSSES.
Pen No.	Mother.				Father.				Offspring.
	No.	Gen.	Races.	Grade.	No.	Gen.	Races.	Grade.	Boot present.	Boot slight.	Boot absent.	P. ct. absent.
608	384	F1	Wh. Legh. × Dk. Brah.	Pr.	409	F1	Wh. Legh. × Dk. Brah.	Pr.	36	5	3	6.8
608	248	F1	Do.	Pr.	409	F1	Do.	Pr.	32	5	4	9.8
608	249	F1	Do.	Pr.	409	F1	Do.	Pr.	39	11	13	20.6
608	395	F1	Do.	Pr.	409	F1	Do.	Pr.	20	11	10	24.4
608	385	F1	Do.	Pr.	409	F1	Do.	Pr.	20	6	14	35.0
			Totals (229)						147	38	44	19.2
659	762	F1	Wh. Legh. × Dk. Brah.	Pr.	375	F1	Wh. Legh. × Dk. Brah.	Pr.	18	4	1	4.4
659	503	F1	Do.	Pr.	375	F1	Do.	Pr.	23	6	2	6.5
659	382	F1	Do.	Pr.	375	F1	Do.	Pr.	10	2	1	7.7
659	250	F1	Do.	Pr.	375	F1	Do.	Pr.	33	7	5	11.1
659	737	F1	Do.	Pr.	375	F1	Do.	Pr.	19	2	3	12.5
659	387	F1	Do.	Pr.	375	F1	Do.	Pr.	16	6	4	15.4
			Totals (162)						119	27	16	9.9
655	720	F1	Wh. Legh. × Dk. Brah.	Pr.	666	F1	Wh. Legh. × Dk. Brah.	Pr.	5	2	...	0.0
655	724	F1	Do.	Pr.	666	F1	Do.	Pr.	6	1	...	0.0
655	728	F1	Do.	Pr.	666	F1	Do.	Pr.	3	1	...	0.0
655	730	F1	Do.	Pr.	666	F1	Do.	Pr.	4	...	...	0.0
655	732	F1	Do.	Pr.	666	F1	Do.	Pr.	9	...	...	0.0
655	734	F1	Do.	Pr.	666	F1	Do.	Pr.	3	...	...	0.0
655	761	F1	Do.	Pr.	666	F1	Do.	Pr.	6	2	...	0.0
655	800	F1	Do.	Pr.	666	F1	Do.	Pr.	1	...	...	0.0
655	721	F1	Do.	Pr.	666	F1	Do.	Pr.	9	1	1	9.1
			Totals (54)						46	7	1	1.9
655	724	F1	Wh. Legh. × Dk. Brah.	Pr.	254	F1	Wh. Legh. × Dk. Brah.	Pr.	3	...	...	0.0
655	734	F1	Do.	Pr.	254	F1	Do.	Pr.	12	1	...	0.0
655	800	F1	Do.	Pr.	254	F1	Do.	Pr.	13	...	1	7.1
655	720	F1	Do.	Pr.	254	F1	Do.	Pr.	12	...	1	7.7
655	728	F1	Do.	Pr.	254	F1	Do.	Pr.	8	1	1	10.0
655	761	F1	Do.	Pr.	254	F1	Do.	Pr.	17	4	4	16.0
655	732	F1	Do.	Pr.	254	F1	Do.	Pr.	8	1	2	18.2
655	730	F1	Do.	Pr.	254	F1	Do.	Pr.	7	...	2	22.2
655	721	F1	Do.	Pr.	254	F1	Do.	Pr.	9	...	3	25.0
			Totals (110)						89	7	14	12.7
632	742	F1	Min. × Dk. Brah.	Pr.	637	F1	Min. × Dk. Brah.	Pr.	4	1	0	0.0
632	690	F1	Do.	Pr.	637	F1	Do.	Pr.	27	6	1	2.9
632	631	F1	Do.	Pr.	637	F1	Do.	Pr.	32	11	2	4.4
632	618	F1	Do.	Pr.	637	F1	Do.	Pr.	35	8	2	4.4
632	700	F1	Do.	Pr.	637	F1	Do.	Pr.	18	3	2	8.7
632	703	F1	Do.	Pr.	637	F1	Do.	Pr.	14	11	3	10.7
632	743	F1	Do.	Pr.	637	F1	Do.	Pr.	22	2	3	11.1
632	599	F1	Do.	Pr.	637	F1	Do.	Pr.	23	8	4	11.4
632	524	F1	Do.	Pr.	637	F1	Do.	Pr.	18	6	5	17.2
632	576	F1	Do.	Pr.	637	F1	Do.	Pr.	14	9	6	20.7
632	638	F1	Do.	Pr.	637	F1	Do.	Pr.	8	2	6	37.5
			Totals (316)						215	67	34	10.8

Pen No.	Mother.				Father.				Boot-grade in offspring.
	No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.	0	1	2	3	4	5	6	7	8	9	10	Aver- age.	P. ct. absent.
801	2526	F1	Min. × Dk. Brah.	2	5399	F1	W. L. × Dr. Brah.	8	...	...	...	...	1	...	...	1	...	...	1	7.0	0.0
801	2831	F1	Do.	4	5399	F1	Do.	8	1	1	1	4	1	7	2	2	2	...	2	5.0	4.3
801	1892	F1	Do.	3	5399	F1	Do.	8	1	1	0	1	2	...	1	...	1	1	1	5.0	11.1
			Totals (35)						2	2	1	5	4	7	3	3	3	1	4	5.2	5.71

Table 34.—Distribution of boot-grade in the F₂ generation of booted × non-booted poultry—Continued.

SILKIE CROSSES.
Pen No.	Mother.				Father.				Boot-grade in offspring.
	No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.	0	1	2	3	4	5	6	7	8	9	10	Aver- age.	P. ct. absent.
709	1955	F1	Silkie × Spanish	5	1578	F1	Silkie × Spanish	0	5	1	2	1	1	1	1	0	0	0	0	1.92	41.7
753	1966	F1	Silkie × Min	0	2573	F1	Min. × Silkie	0	19	4	2	2	...	2	2	2	1	...	...	1.71	55.9
709	1963	F1	Silkie × Spanish	7	1578	F1	Silkie × Spanish	0	23	6	1	6	7	...	...	...	...	...	...	1.26	53.5
753	2575	F1	Silkie × Min	0	2573	F1	Silkie × Min.	0	15	3	7	...	...	...	...	...	...	...	...	0.68	60.0
753	2071	F1	Do.	0	2573	F1	Do.	0	23	4	6	...	...	...	...	...	...	...	...	0.49	69.7
709	1453	F1	Do.	1	1578	F1	Silkie × Spanish	0	24	11	3	...	...	...	...	...	...	...	...	0.45	63.2
709	2223	F1	Silkie × Spanish	0	1578	F1	Do.	0	32	7	3	...	...	...	...	...	...	...	...	0.31	76.2
			Totals (227)						141	36	24	9	8	3	3	2	1	0	0	0.87	62.2
830	4082	F1	Silkie × W. Legh	2	3947	F1	Silkie × W. Legh	1	11	8	...	7	1	...	...	...	...	...	...	1.22	40.7
830	4079	F1	Do.	0	3947	F1	Do.	1	18	7	6	3	...	...	...	...	...	...	...	0.82	53.0
830	5379	F1	Do.	0	3947	F1	Do.	1	18	4	5	3	...	...	...	...	...	...	...	0.77	60.0
830	4081	F1	Do.	0	3947	F1	Do.	1	24	6	10	1	...	...	...	...	...	...	...	0.71	58.5
830	5374	F1	Do.	0	3947	F1	Do.	1	11	3	3	1	...	...	...	...	...	...	...	0.67	61.1
830	3946	F1	Do.	0	3947	F1	Do.	1	19	1	...	...	1	...	...	...	...	...	...	0.24	90.5
			Totals (170)						101	29	24	14	2	0	0	0	0	0	0	0.75	59.4

The distribution of table 35 is characterized by its large variability. Although the numbers are small, there are evidences of two modes, one between grades 3 and 6, and the other at from 8 to 10; these evidently correspond to the modes of the typical Silkie and the typical Cochin respectively or to DR and RR types of booting respectively. The distribution of table 35 is additional evidence of the heterozygous nature of the Silkie boot.

Table 35.—Distribution of boot-grades in Silkie × Cochin crosses.

Pen No.	Mother.				Father.				Boot-grades in offspring.
	No.	Gen.	Races.	Gra.	No.	Gen.	Races.	Gra.	0	1	2	3	4	5	6	7	8	9	10	Aver- age.	P. ct. abs.
821	5925	F1	Silk. × Coch.	7	6095	F1	Silk. × Coch.	7	...	...	...	...	1	...	...	1	3	1	1	7.7	0.0
821	7408	F1	Do.	4	6095	F1	Do.	7	...	...	...	1	2	2	3	...	2	1	2	6.5	0.0
821	7413	F1	Do.	3	6095	F1	Do.	7	2	0	3	1	0	1	1	0	0	1	1	3.9	20.0
821	7416	F1	Do.	5	6095	F1	Do.	7	...	...	...	3	1	0	4	0	3	3	2	6.8	0.0
821	7417	F1	Do.	...	6095	F1	Do.	7	...	...	...	...	...	...	...	1	...	1	4	9.3	0.0
821	7418	F1	Do.	4	6095	F1	Do.	7	...	...	1	...	2	1	1	1	1	...	1	5.8	0.0
821	7423	F1	Do.	6	6095	F1	Do.	7	...	...	...	1	...	2	...	2	2	...	2	7.0	0.0
821	7428	F1	Do.	...	6095	F1	Do.	7	1	...	...	...	...	1	...	...	1	...	...	4.3	33.3
821	7429	F1	Do.	8	6095	F1	Do.	7	...	...	...	1	1	1	...	...	...	1	1	6.2	0.0
			Totals (77)						3	0	4	7	7	8	9	5	12	8	14	6.42	3.90
									29						48

We are now in a position to consider the effect of back crosses (table 36). The contrast between the totals in tables 36 and 37 is very great. The strict Mendelian expectation is: in the DR × D crosses 50 per cent DD (clean-footed) and 50 per cent heterozygous, which, with imperfect dominance, might be expected to show foot-feathering. Actually about 46 per cent are clean-footed. In the DR × R crosses expectation is that 50 per cent certainly (the extracted recessives) and 50 per cent more possibly will have the shanks feathered, on account of imperfect dominance of the heterozygotes. Actually all have feathered feet. These statistics thus confirm the view of the dominance of the inhibiting factor. Were clean shank recessive, then the DR × R crosses must give 50 per cent clean-footed and probably over. The actual result, none clean-footed, is not in accord with the latter assumption.

Table 36.—Distribution of boot-grade in DR × D (non-booted) crosses.

Pen No.	Mother.				Father.				Boot-grade in offspring.
	No.	Gen.	Races.	Grade.	No.	Gen.	Race.	Grade.	Present.	Slight.	Absent.	Per cent. present.
653	508	F1	Wh. Legh. × Bf. Coch.	Pr.	117	P.	Game.	0	3	4	6	46.2
653	508	F1	Do.	Pr.	116	P.	Do.	0	6	5	4	26.7
653	577	F1	R × Bf. Coch.	3	117	P.	Do.	0	1	0	7	87.5
653	577	F1	Do.	3	116	P.	Do.	0	1	3	2	33.3
653	587	F1	Do.	1	117	P.	Do.	0	1	2	4	57.1
653	587	F1	Do.	1	116	P.	Do.	0	3	3	2	25.0
653	635	F1	Do.	3	117	P.	Do.	0	...	1	6	85.7
653	635	F1	Do.	3	116	P.	Do.	0	2	2	1	20.0
653	652	F1	Do.	5	117	P.	Do.	0	5	8	4	23.5
653	652	F1	Do.	5	116	P.	Do.	0	1	2	2	40.0
653	691	F1	Do.	Pr.	117	P.	Do.	0	2	2	1	20.0
653	705	F1	Do.	2	117	P.	Do.	0	3	2	5	50.0
653	705	F1	Do.	2	116	P.	Do.	0	1	1	5	71.4
653	713	F1	Do.	Pr.	117	P.	Do.	0	...	0	4	100.0
653	713	F1	Do.	Pr.	116	P.	Do.	0	1	1	3	60.0
653	760	F1	Do.	Pr.	117	P.	Do.	0	2	2	6	60.0
653	760	F1	Do.	Pr.	116	P.	Do.	0	0	3	2	40.0
653	799	F1	Do.	3	117	P.	Do.	0	2	0	3	60.0
			Total (143)						34	42	67	46.9
661	635	F1	Bf. Coch. × Game.	Pr.	466	P.	Game.	0	1	...	2	66.7
661	635	F1	Do.	Pr.	428	P.	Do.	0	2	...	1	33.3
661	691	F1	Do.	Pr.	466	P.	Do.	0	2	...	2	50.0
661	691	F1	Do.	Pr.	428	P.	Do.	0	2	...	1	33.3
661	799	F1	Do.	Pr.	466	P.	Do.	0	3	...	2	40.0
661	799	F1	Do.	Pr.	428	P.	Do.	0	4	...	1	20.0
			Total (23)						14	0	9	39.1
			Grand Total (166)						48	42	76	45.8

Table 37.—Distribution of boot-grade in DR × RR (booted) crosses.

[A]Pure-blooded Silkie assumed heterozygous to boot.
Pen No.	Mother.				Father.				Boot-grade in offspring.
	No.	Gen.	Race.	Gr.	No.	Gen.	Race.	Gr.	0	1	2	3	4	5	6	7	8	9	10
851	838	P.	Cochin.	8	7526	[A]F1	Silkie.	3	...	...	...	3	2	4	3	...	...	2	2
851	840	P.	Do.	10	7526	F1	Do.	3	...	...	...	...	1	...	1	...	...	1	...
851	841	P.	Do.	10	7526	F1	Do.	3	...	...	...	...	1	...	1	...	1	...	...
851	1002	P.	Do.	8	7526	F1	Do.	3	...	...	...	3	1	2	1	2	3	1	1
851	2073	P.	Do.	7	7526	F1	Do.	3	...	...	1	1	1	...	1	1	1	3	2
851	2299	P.	Do.	9	7526	F1	Do.	3	...	...	...	...	2	2	1	1	...	...	2
851	3410	P.	Do.	9	7526	F1	Do.	3	...	...	...	...	...	4	3	2	1	5	1
851	5567	P.	Do.	9	7526	F1	Do.	3	...	...	...	...	2	...	...	...	3	3	5
851	6956	P.	Do.	8	7526	F1	Do.	3	...	...	...	...	3	3	...	2	2	...	5
			Totals (99)						0	0	1	7	13	15	11	8	11	15	18

Numerous observations have been made upon the progeny of parents belonging to hybrid generations beyond the first. Owing to the extreme imperfection of dominance it is rarely possible to say with certainty from inspection whether a given bird has germ-cells dominant or recessive, or both, with reference to booting; only breeding enables us to make a decision. There is an exception, however, in the case of pure extracted recessives. They are distinguished by heavy booting and produce only booted offspring. I propose to give, in detail, the matings of these later generations and their progeny, the families being arranged in decreasing order of average grade of booting (table 38).

Table 38.—Distribution of boot-grades in offspring of parents one or both of which belong to a hybrid generation beyond the first.

B = Brahma; C = Cochin; G = Game; L = Leghorn; M = Minorca; S = Silkie; Sp = Spanish; T = Tosa; WL = White Leghorn

Serial No.	Pen No.	Mother.				Father.				Mating.	Boot-grade in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		0	1	2	3	4	5	6	7	8	9	10	Av.
1	814	354	F1	B × T	7	3975	F2	B × T	9	R × R	...	...	...	...	...	...	...	...	...	10	15	9.6
2	801	181	F1	Do.	4	5399	F2	M × B	8	Do.	...	...	...	...	...	...	...	...	...	1	1	9.5
3	814	300	F1	Do.	5	3975	F2	B × T	9	Do.	...	...	...	...	...	...	...	...	1	3	4	9.4
4	801	4569	F2	Do.	6	4562	F2	Do.	7	Do.	...	...	...	...	...	...	...	...	1	1	2	9.3
5	814	5523	F2	Do.	9	3975	F2	Do.	9	Do.	...	...	...	...	...	1	...	...	3	4	9	9.1
6	814	4560	F2	Do.	8	3975	F2	Do.	9	Do.	...	...	...	...	...	1	1	1	...	2	7	8.8
7	814	190	F1	Do.	2	3975	F2	Do.	9	Do.	...	...	...	...	...	...		1	1	1	4	8.8
8	806	4325	F3	M × B	7	5257	F3	M × B	9	Do.	...	...	...	...	...	...	1	1	2	2	3	8.6
9	806	5913	F3	Do.	7	5257	F3	Do.	9	Do.	...	...	...	...	1	...	...	1	4	2	3	8.3
10	732	1235	F2	Do.	8	2732	F2	Do.	6	Do.	...	...	...	...	...	...	1	2	4	3	...	7.9
11	806	4052	F3	Do.	5	5257	F3	Do.	5	Do.	...	...	...	...	1	1	...	3	...	6	1	7.8
12	776	1132	F2	C × WL	3	2732	P.	C	8	DR × R	...	...	...	1	1	1	1	3	6	8	...	7.6
13	801	6869	F1.5	B × F1	6	4562	F2	M × B	7	R × R	...	...	...	...	...	1	1	2	1	1	1	7.4
14	814	186	F1	T × B	4	3975	F2	B × T	9	DR × R	...	2	1	0	1	3	0	1	3	6	5	7.2
15	814	4683	F2	Do.	2	3975	F2	Do.	9	Do.	...	...	...	...	3	2	3	1	1	1	5	7.1
16	767	2104	F2	WL × B	3	3116	F1	Do.	9	Do.	...	...	...	1	4	1	2	7	6	1	0	7.1
17	801	2526	F1	Do.	2	5399	F2	M × B	8	Do.	...	...	...	...	1	...	...	1	...	...	1	7.0
18	806	3936	F2	M × B	10	5257	F3	Do.	9	R × R	...	...	...	...	1	...	2	...	2	...	1	7.0
19	839	5383	F2	L × M × B	2	4348	F2	L × M × B	3	DR × DR	...	...	...	...	1	1	...	...	...	1	1	7.0
20	801	5515	F2	B × T	4	5399	F2	M × B	8	DR × R	...	...	...	1	1	2	2	...	1	1	3	6.9
21	732	1003	F2	M × B	9	2442	F2	Do.	6	R × R	...	...	...	...	3	7	7	7	7	5	2	6.8
22	839	1892	F1.5	L × M × B	6	4348	F2	L × M × B	3	R × DR	...	...	...	2	1	...	1	...	...	2	2	6.8
23	806	4196	F3	M × B	2	5257	F3	M × B	9	DR × R	...	...	...	2	2	2	1	...	...	3	3	6.7
24	801	2526	F1	WL × B	2	5399	F2	Do.	8	Do.	...	...	...	...	1	...	...	1	...	1	0	6.7
25	801	6861	F2.5	B × T	7	4562	F2	Do.	7	R × R	...	...	...	...	...	2	1	...	...	...	1	6.5
26	767	872	F2	Do.	5	3116	F1	B × T	9	DR × R	1	0	0	1	4	6	9	4	4	6	3	6.5
27	801	4263	F2	Do.	3	4562	F2	M × B	7	Do.	...	...	...	2	3	...	3	1	1	4	1	6.5
28	767	181	F1	Do.	4	3166	F1	B × T	9	Do.	...	...	1	2	6	13	11	5	11	8	3	6.5
29	814	862	F2	Do.	1	3975	F2	Do.	9	Do.	...	...	...	2	2	5	2	1	1	3	2	6.3
30	801	872	F2	Do.	5	5399	F2	M × B	8	Do.	...	...	...	1	3	8	5	2	...	2	4	6.3
31	839	5389	F2	M × B	7	4348	F2	Do.	3	R × DR	...	...	...	6	4	1	0	1	1	1	6	6.2
32	801	872	F2	B × T	5	4562	F2	Do.	7	DR × R	...	...	...	1	5	4	3	1	2	2	2	6.1
33	767	190	F1	Do.	4	3116	F1	B × T	9	Do.	...	...	...	5	6	11	12	7	4	9	...	6.1
34	801	1892	F1	M × B	3	4562	F2	M × B	7	Do.	...	...	1	...	...	...	1	...	2	...	...	6.0
35	801	5515	F2	B × T	4	4562	F2	Do.	7	Do.	...	...	1	...	...	1	3	...	1	1	...	6.0
36	731	248	F1	M × B	4	1249	F2	WL × B	7	Do.	...	...	2	3	3	...	2	...	...	5	2	6.0
37	732	1228	F2	Do.	8	2442	F2	M × B	6	R × R	...	...	...	2	8	5	6	2	8	3	...	6.0
38	732	690	F1	Do.	5	2442	F2	Do.	6	DR × R	2	0	6	2	5	5	7	16	10	6	...	6.0
39	751	1919	F2	WL × B	8	1139	F2	L × B	8	R × R	...	...	...	5	4	6	6	1	11	1	...	5.9
40	732	618	F1	M × B	8	2442	F2	M × B	6	DR × R	...	1	2	3	2	5	3	5	9	1	...	5.8
41	731	1245	F2	WL × B	9	1249	F2	WL × B	7	R × R	...	...	1	2	1	8	2	3	6	...	...	5.8
42	760	354	F1	B × T	5	1270	F2	B × T	2	R × DR	...	...	1	3	9	5	8	4	7	2	...	5.7
43	701	1915	F2	WL × B	8	1898	F2	WL × B	3	Do.	...	...	...	...	7	4	3	2	3	1	...	5.7
44	801	6869	F1.5	B (M × B)	6	5399	F2	Do.	8	DR × R	...	...	...	1	...	1	...	...	...	1	...	5.7
45	801	4570	F2	B × T	2	4562	F2	Do.	7	Do.	...	...	1	2	5	3	1	1	1	4	...	5.6
46	814	703	F1	Do.	4	3975	F2	B × T	9	Do.	...	...	3	5	2	7	5	6	2	4	...	5.5
47	732	953	F2	M × B	3	2442	F2	M × B	6	Do.	...	2	2	3	8	9	5	3	7	6	...	5.5
48	801	7528	F1	Do.	4	4562	F2	Do.	8	Do.	...	...	...	1	4	2	1	...	1	...	1	5.3
49	731	2116	F2	Do.	10	1249	F2	WL × B	7	R × R	...	1	1	1	2	3	0	2	2	1	...	5.2
50	745	2115	F2	C × T	4	1258	F2	B × T	4	DR × DR	...	...	...	2	1	6	4	2	...	...	...	5.2
51	801	6843	F2	B × T	3	4562	F2	Do.	8	DR × R	...	...	...	...	3	2	1	...	1	...	...	5.1
52	801	2831	F1	M × B	4	5399	F2	Do.	8	Do.	1	1	1	4	1	7	2	2	2	...	2	5.0
53	801	1892	F1	Do.	3	5399	F2	Do.	8	Do.	1	1	...	1	2	...	1	0	1	1	1	5.0
54	801	7528	F1	Do.	4	4562	F2	Do.	8	Do.	...	...	...	1	2	1	1	...	1	...	...	5.0
55	731	1755	F2	WL × B	6	1249	F2	WL × B	7	R × R	...	...	...	...	2	1	4	1	2	...	...	5.0
56	745	2513	F3	C × T	4	1258	F2	B × T	4	DR × DR	...	...	...	...	2	5	2	...	3	1	...	5.0
57	839	3950	F2	M × B	4	4348	F2	M × B	3	Do.	...	2	3	3	2	4	1	1	1	2	2	4.95
58	754	873	F2	B × T	3	871	F2	B × T	2	Do.	1	2	1	4	1	...	...	...	8	...	...	4.94
59	806	599	F2	M × B	3	5257	F2	M × B	7	DR × R	...	...	2	1	2	2	1	...	1	...	...	4.86
60	760	300	F1	B × T	7	1270	F2	B × T	2	R × DR	...	...	2	19	8	13	6	4	5	2	1	4.83
61	806	4456	F2	M × B	1	5257	F3	M × B	7	DR × R	...	1	1	1	1	...	1	...	1	1	...	4.71

Table 38.—Distribution of boot-grades in offspring of parents one or both of which belong to a hybrid generation beyond the first—Continued.

B = Brahma; C = Cochin; G = Game; L = Leghorn; M = Minorca; S = Silkie; Sp = Spanish; T = Tosa; WL = White Leghorn.

Serial No.	Pen No.	Mother.				Father.				Mating.	Boot-grade in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		0	1	2	3	4	5	6	7	8	9	10	Av.
62	732	2407	F2	M × B	2	2442	F2	M × B	6	DR × R	...	...	1	3	4	1	1	2	...	1	...	4.69
63	701	894	F2	L × B	7	1898	F2	L × B	3	R × DR	1	1	2	8	6	1	2	2	4	2	...	4.62
64	760	994	F2	B × T	3	1270	F2	B × T	3	DR × DR	...	...	...	...	4	2	1	...	...	...	...	4.57
65	760	981	F2	Do.	3	1270	F2	Do.	3	Do.	1	...	3	6	1	4	2	7	...	...	...	4.54
66	701	1772	F2	L × B	6	1898	F2	L × B	3	R × DR	...	...	...	4	7	2	2	2	...	...	...	4.47
67	839	3541	F1	M × B	6	4348	F2	M × B	3	DR × DR	4	1	4	...	...	4	2	...	2	1	2	4.30
68	842	1645	F2	Do.	2	4385	F2	Do.	4	Do.	3	2	6	5	6	6	3	0	2	4	1	4.29
69	770	2049	F2	L × B	3	926	F2	Do.	3	Do.	9	3	1	6	8	2	6	6	3	1	3	4.29
70	731	2577	F1.5	L × C	4	1249	F2	L × B	7	DR × R	...	...	2	2	3	2	2	1	...	...	...	4.25
71	701	250	F1	L × B	3	1898	F2	Do.	3	DR × DR	3	3	5	8	12	10	10	6	1	...	...	4.22
72	701	1335	F2	T × L × B	8	1898	F2	Do.	3	R × DR	...	...	1	9	6	6	4	1	...	...	...	4.22
73	806	4767	F3	M × B	3	5257	F3	M × B	7	DR × R	...	...	1	...	2	1	1	...	...	...	...	4.20
74	740	1439	F2	C × L	2	1145	F2	C × L	3	DR × DR	3	...	1	3	6	4	2	...	2	1	...	4.18
75	754	3126	F2	B × T	4	871	F2	B × T	3	Do.	...	2	5	11	7	10	5	0	2	1	...	4.14
76	770	1645	F2	M × B	4	926	F2	M × B	3	Do.	3	2	1	9	5	5	2	2	3	1	...	4.10
77	731	249	F1	L × B	3	1249	F2	L × B	7	DR × R	7	4	6	5	7	5	9	3	6	1	...	4.08
78	732	703	F1	M × B	3	2442	F2	M × B	6	Do.	1	3	13	13	8	6	7	6	3	...	...	4.07
79	770	720	F1	B × L	4	926	F2	Do.	3	DR × DR	6	1	3	9	5	4	5	1	4	1	1	4.05
80	732	2441	F2	M × B	0	2442	F2	Do.	6	DR × R	...	1	6	8	2	6	0	3	1	...	...	4.00
81	760	1042	F2	B × T	3	1270	F2	B × T	2	DR × DR	2	3	3	9	3	5	8	2	0	1	...	4.00
82	731	384	F1	L × B	4	1249	F2	L × B	7	DR × R	2	1	4	4	3	2	4	0	1	1	...	3.82
83	814	4566	F2	B × T	2	3975	F2	B × T	9	Do.	1	4	2	4	3	2	1	...	...	...	...	3.82
84	732	599	F1	M × B	3	2442	F2	M × B	6	Do.	6	5	23	10	5	3	4	5	8	3	1	3.78
85	770	761	F1	B × L	3	926	F2	Do.	3	DR × DR	7	3	5	3	7	7	2	6	1	1	...	3.71
86	731	1770	F2	Do.	7	1249	F2	L × B	7	DR × R	1	...	8	6	9	3	2	...	2	...	...	3.65
87	861	5165	F2	T × C	10	95	F1	T × C	5	R × DR	...	...	...	10	3	2	1	...	...	...	...	3.63
88	754	3175	F2	B × T	2	871	F2	B × T	2	DR × DR	1	...	2	1	3	4	...	...	...	...	...	3.55
89	731	2102	F2	L × B	1	1249	F2	L × B	7	DR × R	1	0	4	2	4	1	1	1	...	...	...	3.43
90	840	1755	F2	M × B	6	4177	F2	Do.	2	R × DR	...	...	6	7	7	3	1	...	...	...	...	3.42
91	701	2576	F2	L × B	2	1898	F2	Do.	3	DR × DR	2	1	1	8	11	2	1	...	...	...	...	3.35
92	842	2049	F1	Do.	3	4385	F2	M × B	4	Do.	11	1	2	8	5	3	1	0	2	2	2	3.35
93	754	853	F2	B × T	1	871	F2	B × T	3	Do.	2	3	4	6	4	1	6	...	...	...	...	3.31
94	826	2652	F1	M × B	3	4093	F2	M × B	0	Do.	8	2	1	8	1	...	...	1	2	3	...	3.28
95	754	1052	F2	B × T	2	871	F2	B × T	2	Do.	3	...	7	9	9	5	2	...	...	...	...	3.26
96	701	965	F2	T × L × B	0	1898	F2	L × B	3	Do.	1	4	6	12	8	4	0	2	0	...	...	3.19
97	732	1833	F2	M × B	1	2442	F2	M × B	6	DR × R	1	1	7	6	6	4	1	...	...	...	...	3.19
98	732	631	F1	Do.	3	2442	F2	Do.	6	Do.	3	4	10	16	12	4	1	2	...	...	...	3.08
99	754	862	F2	B × T	1	871	F2	B × T	2	DR × DR	1	5	10	17	10	4	1	...	...	...	...	2.96
100	837	5641	F2	T × L × B	0	4288	F3	L × B	2	Do.	1	2	2	3	...	2	...	1	...	...	...	2.91
101	840	3841	F2	L × B	0	4177	F2	Do.	2	D × DR	3	3	2	6	4	2	...	...	...	...	...	2.86
102	701	721	F1	Do.	2	1898	F2	Do.	3	DR × DR	2	4	3	8	3	2	2	...	...	...	...	2.83
103	839	3949	F2	Do.	4	4348	F2	Do.	3	Do.	1	2	...	...	1	1	1	...	...	...	...	2.83
104	840	732	F1	Do.	3	4177	F2	Do.	2	Do.	7	6	9	8	7	2	1	2	...	1	...	2.67
105	840	249	F1	Do.	3	4177	F2	Do.	2	Do.	7	3	5	6	2	9	...	...	...	...	...	2.62
106	840	3916	F1.5	Do.	2	4177	F2	Do.	2	Do.	5	1	4	2	2	2	1	...	...	...	...	2.29
107	842	4945	F2	M,L × B	1	4385	F2	M × B	4	Do.	9	3	6	5	1	2	4	...	...	...	...	2.27
108	731	2595	F2	L × B	1	1249	F2	L × B	7	D × R	6	6	7	1	...	...	...	...	...	...	...	2.15
109	840	5169	F2	Do.	3	4177	F2	Do.	2	DR × DR	6	2	5	5	2	2	...	...	...	...	...	2.05
110	837	5667	F3	Do.	2	4288	F3	Do.	2	Do.	2	1	2	...	1	1	...	...	...	...	...	2.00
111	749	1355	F2	G × C	2	1854	F2	G(C × L)	0	DR × D	...	2	5	1	...	...	...	...	...	...	...	1.87
112	824	3901	F2	M × S	1	5095	F2	M × S	1	DR × DR	17	3	2	3	...	2	...	...	1	2	...	1.73
113	751	1254	F2	L × B	0	1139	F2	L × B	8	D × R	17	5	5	4	3	3	...	1	...	...	...	1.63
114	749	816	F1	Do.	2	1854	F2	G(C × L)	0	DR × D	6	7	3	5	1	...	...	...	...	...	...	1.45
115	749	929	F2	G × C	0	1854	F2	Do.	0	D × D	8	3	1	...	...	...	1	...	...	1	...	1.43
116	749	819	F1	L × B	1	1854	F1.5	G(C × L)	0	DR × D	9	3	5	3	...	...	...	...	...	...	...	1.10
117	804	5099	F2	S × Sp	0	3823	F1	S × Sp	0	D × D	2	...	...	1	...	...	...	...	...	...	...	1.00
118	804	6043	F2	Do.	1	3823	F1	Do.	0	Do.	...	1	...	...	...	...	...	...	...	...	...	1.00
119	817	5730	F1	L × Sp	0	3900	F2	Do.	1	D × DR	3	3	1	...	...	...	...	...	...	...	...	0.71
120	817	4696	F1	Do.	0	3900	F2	Do.	1	Do.	9	7	3	...	...	...	...	...	...	...	...	0.68
121	817	6046	F2	S × M	0	3900	F2	Do.	1	Do.	10	...	3	...	...	...	...	...	...	...	...	0.46
122	817	6833	F1.5	L(G × S)	0	3900	F2	Do.	1	Do.	6	2	1	...	...	...	...	...	...	...	...	0.44
123	817	5062	F1	L(Sp)	0	3900	F2	Do.	1	Do.	18	7	2	...	...	...	...	...	...	...	...	0.41
124	817	5069	F1	Do.	0	3900	F2	Do.	1	Do.	21	7	2	...	...	...	...	...	...	...	...	0.37
125	817	6406	F1	Do.	0	3900	F2	Do.	1	Do.	25	8	2	...	...	...	...	...	...	...	...	0.34
126	817	7047	F1	Do.	0	3900	F2	Do.	1	Do.	4	2	...	...	...	...	...	...	...	...	...	0.33
127	749	2651	F2	G × C	0	1854	F2	G(C × L)	0	D × D	2	1	...	...	...	...	...	...	...	...	...	0.33
128	824	4714	F2	S × Sp	0	5095	F2	M × S	1	Do.	26	6	1	1	...	...	...	...	...	...	...	0.32
129	817	4690	F1	Do.	0	3900	F2	S × Sp	1	D × DR	21	6	1	...	...	...	...	...	...	...	...	0.29
130	824	7439	F2	Do.	0	5095	F2	M × S	1	D × D	11	4	...	...	...	...	...	...	...	...	...	0.27
131	804	4715	F2	Do.	0	3823	F1	S × Sp	0	DR × DR	18	2	1	...	...	...	...	...	...	...	...	0.19
132	804	3898	F2	S × M	0	3823	F1	Do.	0	D × DR	19	...	...	...	...	...	...	...	...	...	...	0.00
133	804	3902	F2	Do.	0	3823	F1	Do.	0	Do.	33	...	...	...	...	...	...	...	...	...	...	0.00
134	804	4657	F2	Do.	0	3823	F1	Do.	0	Do.	8	...	...	...	...	...	...	...	...	...	...	0.00
135	804	4716	F2	Do.	0	3823	F1	Do.	0	Do.	19	...	...	...	...	...	...	...	...	...	...	0.00
136	804	5431	F2	Do.	0	3823	F1	Do.	0	Do.	16	...	...	...	...	...	...	...	...	...	...	0.00

In table 38 I have given in the section lying between that headed "Father" and that headed "Offspring" the "Matings." This column differs from the others of the table in not being, in general, based upon observation, but upon a sometimes complicated judgment. Of course, all of the F₁ generation, where this generation occurs, may be taken as of DR composition; but the decision as to whether a given individual of F₂ is a DR, an extracted dominant, or an extracted recessive is not always easy, because of the manifestation of imperfect dominance. But the assignments are by no means arbitrary. Taking the Brahma crosses, which are by far the most numerous, we see, from tables 31, B and 33, that those F₂ individuals that have a boot of grade 6 or higher are almost certainly extracted recessives (which are equivalent to pure-bred Dark Brahmas). Those with a grade of 3 or even 4 and lower to 2 or even 1 are probably heterozygotes, while those with grade 0 and some of those with grade 1 are extracted dominants. In cases of doubt the distribution of grades in the offspring will give the deciding vote. In case the individual has been used as a parent in more than one mating the results in all the matings are taken into account, for the germinal constitution of an individual must be regarded as fixed at all times and in all matings. The assignment under "Matings" has, then, been made by the application of the above rules.

In tables 39 to 43 there are grouped together the progeny from matings of the same sort, selecting from table 38 the crosses into which the Dark Brahma enters as the booted parent.

Table 39.—RR × RR crosses from table 38.

Serial No.	Boot-grade in offspring.												Parental grades.
	0	1	2	3	4	5	6	7	8	9	10	Avge.	Female.	Male.	Average.
1	...	...	...	...	...	...	...	...	...	10	15	9.6	7	9	8.0
2	...	...	...	...	...	...	...	...	...	1	1	9.5	4	8	6.0
3	...	...	...	...	...	...	...	...	1	3	4	9.4	5	9	7.0
4	...	...	...	...	...	...	...	...	1	1	2	9.3	6	7	6.5
5	...	...	...	...	...	1	...	...	3	4	9	9.1	9	9	9.0
6	...	...	...	...	...	1	1	1	...	2	7	8.8	8	9	8.5
7	...	...	...	...	...	...	1	1	1	1	4	8.8	2	9	5.5
8	...	...	...	...	...	...	1	1	2	2	3	8.6	7	5	6.0
9	...	...	...	...	1	...	...	1	4	2	3	8.3	7	5	6.0
10	...	...	...	...	...	...	1	2	4	3	...	7.9	8	6	7.0
11	...	...	...	...	1	1	...	3	...	6	1	7.8	5	5	5.0
13	...	...	...	...	...	1	1	2	1	1	1	7.4	6	7	6.5
18	...	...	...	...	1	...	2	...	2	...	1	7.0	10	9	9.5
21	...	...	...	...	3	7	7	7	7	5	2	6.8	9	6	7.5
25	...	...	...	...	...	2	1	...	...	...	1	6.5	7	7	7.0
37	...	...	...	2	8	5	6	2	7	3	...	6.0	8	6	7.0
39	...	...	...	5	4	6	6	1	11	1	...	5.9	8	8	8.0
41	...	...	1	2	1	8	2	3	6	...	...	5.8	9	7	8.0
49	...	1	1	1	2	3	...	2	2	1	...	5.2	10	7	8.5
55	...	...	...	2	1	4	1	2	...	...	...	5.0	6	7	6.5
Totals (287)	...	1	2	12	22	39	30	28	53	46	54	7.25
Per cent.	...	0.3	0.7	4.2	7.7	13.6	10.5	9.8	18.5	16.0	18.8	...

Table 40.—DR × RR crosses from table 38.

Serial No.	Boot-grade in offspring.
	0	1	2	3	4	5	6	7	8	9	10	Average.
14	...	2	1	...	1	3	...	1	3	6	5	7.2
15	...	...	...	...	3	2	3	1	1	1	5	7.1
16	...	...	...	1	4	1	2	7	6	1	...	7.1
17	...	...	...	...	1	...	...	1	...	...	1	7.0
20	...	...	...	1	1	2	2	...	1	1	3	6.9
22	...	...	...	2	1	...	1	...	...	2	2	6.8
23	...	...	...	2	2	2	1	...	...	3	3	6.7
24	...	...	...	...	1	...	...	1	...	1	...	6.7
26	1	...	...	1	4	6	9	4	4	6	3	6.5
27	...	...	...	2	3	...	3	1	1	4	1	6.5
28	...	...	1	2	6	13	11	5	11	8	3	6.3
29	...	...	...	2	2	5	2	1	1	3	2	6.3
30	...	...	...	1	3	8	5	2	...	2	4	6.3
31	...	...	...	6	4	1	...	1	1	1	6	6.2
32	...	...	...	1	5	4	3	1	2	2	2	6.1
33	...	...	...	5	6	11	12	7	4	9	...	6.1
34	...	...	1	...	...	...	1	...	2	...	...	6.0
35	...	...	1	...	...	1	3	...	1	1	...	6.0
36	...	...	2	3	3	...	2	...	...	5	2	6.0
40	...	1	2	3	2	5	3	5	9	1	...	5.8
42	...	...	1	3	9	5	8	4	7	2	...	5.7
43	...	...	...	...	7	4	3	2	3	1	...	5.7
44	...	...	...	1	...	1	...	...	...	1	...	5.7
45	...	...	1	2	5	3	1	1	1	4	...	5.6
46	...	...	3	5	2	7	5	6	2	4	...	5.5
47	...	2	2	3	8	9	5	3	7	6	...	5.5
48	...	...	...	1	4	2	1	...	1	...	1	5.3
51	...	...	...	...	3	2	1	...	1	...	...	5.1
52	1	1	1	4	1	7	2	2	2	...	2	5.0
53	1	1	...	1	2	...	1	...	1	1	1	5.0
54	...	...	...	1	2	1	1	...	1	...	...	5.0
59	...	...	2	1	2	2	1	...	1	...	...	4.9
60	...	...	2	19	8	13	6	4	5	2	1	4.8
61	...	1	1	1	1	...	1	...	1	1	...	4.8
62	...	...	1	3	4	1	1	2	...	1	...	4.7
63	1	1	2	8	6	1	2	2	4	2	...	4.6
66	...	...	...	4	7	2	2	2	...	...	...	4.5
70	...	...	2	2	3	2	2	1	...	...	...	4.3
72	...	...	1	9	6	6	4	1	...	...	...	4.2
73	...	...	1	...	2	1	1	...	...	...	...	4.2
77	7	4	6	5	7	5	9	3	6	1	...	4.1
78	1	3	13	13	8	6	7	6	3	...	...	4.1
80	...	1	6	8	2	6	...	3	1	...	...	4.0
82	2	1	4	4	3	2	4	...	1	1	...	3.8
83	1	4	2	4	3	2	1	...	...	...	...	3.8
84	6	5	23	10	5	3	4	5	8	3	1	3.8
86	1	...	8	6	9	3	2	...	2	...	...	3.7
89	1	...	4	2	4	1	1	1	...	...	...	3.4
90	...	...	6	7	7	3	1	...	...	...	...	3.4
97	1	1	7	6	6	4	1	...	...	...	...	3.2
98	3	4	10	16	12	4	1	2	...	...	...	3.1
Total (1199)	27	32	117	181	200	172	142	88	105	87	48	5.04
Per cent.	2.3	2.7	9.8	15.1	16.7	14.3	11.9	7.3	8.8	7.2	4.0	...

Table 41.—DR × DD crosses.

Serial No.	Boot-grade in offspring.
	0	1	2	3	4	5	Average.
101	3	3	2	6	4	2	2.9
113	6	7	3	5	1	...	1.5
116	9	3	5	3	...	...	1.1
Total (62)	18	13	10	14	5	2	1.69
Per cent.	29.5	21.3	16.4	23.0	8.2	1.6	...

Table 42.—DR x DR crosses.

Serial No.	Boot-grade in offspring.
	0	1	2	3	4	5	6	7	8	9	10	Average.
19	...	...	...	...	1	1	...	...	...	1	...	7.0
54	...	...	...	2	1	6	4	2	...	...	...	5.2
56	...	...	...	2	5	2	...	3	1	...	...	5.0
57	...	2	3	3	2	4	1	1	1	2	2	5.0
58	1	2	1	4	1	...	...	...	8	...	...	4.9
59	...	...	2	1	2	2	1	...	1	...	...	4.9
64	...	...	...	...	4	2	1	...	...	...	...	4.6
65	1	...	3	6	1	4	2	7	...	...	...	4.5
67	4	1	4	...	...	4	2	...	2	1	2	4.3
68	3	2	6	5	6	6	3	...	2	4	1	4.3
69	9	3	1	6	8	2	6	6	3	1	3	4.3
71	...	...	2	2	3	2	2	1	...	...	...	4.3
75	...	2	5	11	7	10	5	...	2	1	...	4.1
76	3	2	1	9	5	5	2	2	3	1	...	4.1
79	6	1	3	9	5	4	5	1	4	1	1	4.1
81	2	3	3	9	3	5	8	2	...	1	...	4.0
85	7	3	5	3	7	7	2	6	1	1	...	3.7
88	1	...	2	1	3	4	...	...	...	...	...	3.6
91	2	1	1	8	11	2	1	...	...	...	...	3.4
92	11	1	2	8	5	3	1	...	2	2	2	3.4
93	2	3	4	6	4	1	6	...	...	...	...	3.3
94	8	2	1	8	1	...	...	1	2	3	...	3.3
95	3	...	7	9	5	2	...	...	...	...	...	3.3
96	1	4	6	12	8	4	...	2	...	...	...	3.2
99	1	5	10	17	10	4	1	...	...	...	...	3.0
100	1	2	2	3	...	2	...	1	...	...	...	2.9
102	2	4	3	8	3	2	2	...	...	...	...	2.8
103	1	2	...	...	1	1	1	...	...	...	...	2.8
104	7	6	9	8	7	2	1	2	...	1	...	2.7
105	7	3	5	6	2	9	...	...	...	...	...	2.6
106	5	1	4	2	2	2	1	...	...	...	...	2.3
107	9	3	6	5	1	2	4	...	...	...	...	2.3
109	6	2	5	5	2	2	...	...	...	...	...	2.1
110	2	1	2	...	1	1	...	...	...	...	...	2.0
Total (851)	105	61	108	178	127	109	62	37	32	20	12	3.59
Per cent.	12.3	7.2	12.7	20.9	14.9	12.8	7.3	4.4	3.8	2.3	1.4	...

Table 43.—DD x DD (Silkie crosses).

Serial No.	Boot-grade in offspring.
	0	1	2	3	Average.
117	2	...	...	1	1.00
118	...	1	...	...	1.00
128	26	6	1	1	0.32
130	11	4	...	...	0.27
131	18	2	1	...	0.19
132	19	...	...	...	0.0
133	33	...	...	...	0.0
134	8	...	...	...	0.0
135	19	...	...	...	0.0
136	16	...	...	...	0.0
Total (169)	152	13	2	2	0.14
Per cent.	89.9	7.7	1.2	1.2	...

The significance of the data given in tables 39 to 43 is best brought out by summarizing them. Especially instructive is a comparison of the pure-bred with the hybrids. Since the data are most complete in the case of the Brahma crosses, these will be considered in most detail. So far as they go, the results with the Cochins and Silkies are entirely confirmatory.

Table 44 shows clearly, first, that there are families of two booted parents that never fail to produce booted offspring. There is, however, even in pure-bred booted races, a marked variability in the grade of booting, extending from 3 (or 4) to 10. The significance of this variability must be left for future investigations. There is in the least boot, as it were, an extension of the field of activity of the feather-inhibiting factor that is always present on the hinder aspect of the shank, so that it interferes with the development of feathers on the inner face of the shank also.

In the first hybrid generation all somatic cells are hybrid. The feather inhibitor is present in the skin of the shank, but its strength is diluted by the presence in the same cells of a protoplasm devoid of the inhibiting property. Consequently, the prevailing grade of the boot falls from 6 (or 10) to 3. Despite the dilution, inhibition is complete in about 8 per cent of the offspring (grade 0); in about 10 per cent of the offspring the inhibiting factor is so weak that the boot develops as in the pure-blooded Brahma. When, as a result of inbreeding F₁'s, the feather-inhibiting factor is eliminated from certain offspring, and such full-feathered birds are bred together, we find a return of the mode to high numbers, such as 8 to 10 (but also 5). There is no doubt of segregation.

Table 44.—Brahma crosses. (All entries are percentages.)

Percentage.	From table.	Boot-grade in offspring.
		0	1	2	3	4	5	6	7	8	9	10	Average grade.
Pure blood	31, B	...	...	...	3.3	3.3	6.6	24.6	4.9	9.8	14.8	32.8	7.62
F1 (D × R)	32	7.9	13.8	16.8	31.0	17.5	7.8	3.4	1.1	0.7	...	...	2.84
Extracted R × R	39	...	0.3	0.7	4.2	7.7	13.6	10.5	9.8	18.5	16.0	18.8	7.25
DR × RR	40	2.3	2.7	9.8	15.1	16.7	14.3	11.9	7.3	8.8	7.2	4.0	5.04
		50 p. ct. DR.					50 p. ct. RR.
DR × DR	42	12.3	7.2	12.7	20.9	14.9	12.8	7.3	4.4	3.8	2.3	1.4	3.59
		25 p. ct. DD.		50 p. ct. DR.				25 p. ct. RR.
DR × DD	41	29.5	21.3	16.4	23.0	8.2	1.6	...	...	...	...	...	1.69
		50 p. ct. DD.		50 p. ct. DR.

If a heterozygous bird be mated to a recessive the variability of the offspring is much increased, owing to the occurrence in the progeny of both DR and RR individuals (table 40). The offspring do not, to be sure, fall into two distinct and well-defined types, as in typical Mendelian cases; but one part of the range of variation agrees fairly with that of pure RR's, i. e., Brahmas, and the remainder with that of heterozygotes. And if we make the division in the middle of the middle class, viz, 5, we shall find a close approximation to that equality of extracted recessives and heterozygotes that the segregation theory calls for (table 44).

If, again, two heterozygous birds be mated, the variability is still greater and the proportion of clean-footed offspring rises to 12 per cent. These, together with some of the extremely slightly booted offspring, represent the extracted dominants. The whole range now falls into three regions divided by the middle of grades 2 and 5. These regions correspond to the DD's, the DR's, and the RR's of typical cases of segregation, and their relative proportions are approximately as 25: 50: 25.

Finally, if a heterozygote be mated to an extracted dominant the proportion of clean-footed offspring rises to about 30 per cent and the whole range of variation falls readily into two parts, the one comprising grades 0 and 1, the other grades 2 and above. The first includes the DD offspring; the second, the DR's; and their frequency is equal. One will not fail to note that we are not here dealing with a case of blending simply, and the inheritance of the blend; such a view is negatived by the fact of the much greater variability of DR × DR cross over the simple D × R cross of the first generation. One may safely conclude, then, that, despite the apparent blending of booting characters in the first generation of hybrids, true segregation takes place. But this is always to be seen through the veil of imperfect dominance.

A casual examination of table 38 would seem to show a correlation between the grade of booting of the parents and that of the average of their progeny. Thus, on the whole, the parental grades run high in the upper part of the table and run low in the lower part. This relation would thus seem to confirm Castle's conclusion for polydactylism in guinea-pigs that there is an inheritance of the degree of a character. One consequence of such an inheritance would be that it would be possible in a few generations to increase or diminish the grade of a character and fix any required grade in the germ-plasm. A more careful consideration of the facts of the case shows that this relation has another interpretation. The grade of boot of the different parents varies largely because their gametic constitution is diverse. As table 39 shows, the parents of the upper part of table 38 are chiefly extracted recessives, and consequently their booting and that of their offspring are characterized by high grades. On the other hand, the parents of the lower part of the table are heterozygous or extracted dominants and, consequently, their grades and also those of their offspring average low. On account of the lack of homogeneity of the families in table 38, one can draw from it no proper conclusions as to relation between parental and filial grades. On the other hand, from a homogeneous table, like table 39, we can hope to reach a conclusion as to the existence of such a relation. I have calculated, in the usual biometric fashion, the coefficient of correlation between average parental and filial grades, and found it to be -0.17 ± 0.13. This can only be interpreted to mean that in a homogeneous assemblage of families there is no correlation between the grade of booting of parents and offspring.

CHAPTER VII.
NOSTRIL-FORM.

In my 1906 report I described in detail the form of the nostril in poultry. Usually it is closed down to a narrow slit, but in some races, as, e. g., the Polish and Houdans, the closing flap of skin fails to develop and the nostril remains wide open. This is apparently an embryonic condition. Thus in Keibel and Abraham's (1900) Normaltafeln of the fowl it is stated that the outer nasal opening, which is at first wide open, becomes closed with epithelium at about the middle of the sixth day of development. The Polish and Houdan fowl thus retain in the outer nasal opening an embryonic condition. The question is: How does this embryonic, open condition of the nostril behave in heredity with reference to the more advanced narrow-slit condition?

The wide-nostriled races used were both the Polish and the Houdan. The condition of the external nares is much the same in the two, but is slightly more exaggerated in the Houdans than in the Polish. The open nostril is often associated with a fold across the culmen, apparently due to the upturning of the anterior end of the premaxillary process of the nasal bone. Breeders of Houdans have sought to exaggerate the height of the fold. In both races there is great variability in the degree of "openness" of the nostril, and to indicate this I have adopted a scale of 10 grades (running from 1, the narrowest, to 10, the widest). To get some idea of this variability let us consider the grade of nostril in some families of pure Houdans.

Table 45.—Variability (expressed in decimal grades) of the degree of "openness" of the nostrils in families of "pure-bred" Houdans.

Serial No.	Pen No.	Mother.		Father.		Grade of openness in offspring.
		No.	Grade.	No.	Grade.	1	2	3	4	5	6	7	8	9	10
1	727	2457	9	831	10	...	...	...	...	...	...	...	...	5	4
2	727	2459	10	831	10	...	...	1	...	...	...	1	3	7	3
3	727	2494	9	831	10	...	...	...	...	...	...	...	...	1	4
4	727	3105	9	831	10	...	1	...	1	2	1	...	5	7	3
5	727	3106	9	831	10	...	...	...	...	...	...	...	...	2	1
6	803	2457	8	7522	9	...	1	1	...	...	2	4	7	10	3
7	803	2459	10	7522	9	...	...	...	...	...	...	1	6	4	2
8	803	3105	9	7522	9	1	...	...	...	4	2	2	7	3	7
	Totals (119)					1	2	2	1	6	5	8	28	39	27
	Percentages.					5.3				5.3	4.4	7.1	24.8	34.5	23.9

Table 45 shows that the prevailing grade in the offspring of pure Houdans is 9; that grades 8 and 10 are also extremely common; and that lower grades, even down to 1, may occur, but these are much less common.

We have next to consider the grade-distribution of the offspring of the narrow mated with the wide nostril.

Table 46.—Distribution of the frequency of the different grades of "openness" of nostril when one parent has the open nostril and the other the closed.

[A] Extracted D × R.
Serial No.	Pen No.	Mother.				Father.				Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.	1	2	3	4	5	6	7	8	9	10
9	727	121	P.	Dk. Brahma.	1	831	P.	Houdan	10	9	11	6	6	2	3	1	1	...	...
10	735	142	P.	Mediterran.	1	30	P.	Polish	8	4	1	...	...	...	...	...	...	...	...
11	735	177	P.	Do.	1	30	P.	Do.	8	...	4	2	1	...	...	...	...	...	...
12	735	198	P.	Do.	1	30	P.	Do.	8	...	3	1	...	...	1	...	...	...	...
				Totals (56)						13	19	9	7	2	4	1	1	...	...
				Percentages						23.2	34.0	16.1	12.5	3.6	7.1	1.8	1.8	...	...
[A]12a	813	912	F2	Houd × Legh.	2	3904	F2	Houd × Legh.	7	3	10	3	1	1	...	...	...	...	...

Table 46 gives us a picture of the nature of the dominance in this case. At first sight the narrow nostril, grades 1 and 2, including 57 per cent of the offspring, appears to be dominant. But, as later evidence shows, it is recessive. The wide nostril is dominant, but so imperfectly that only 10 per cent have a nostril above one-half open.

Let us now consider the distribution of nostril form in families whose parents are hybrids of the first or later generation, crossed respectively on recessives, heterozygotes, and dominants (tables 47-49).

Table 47.—Distribution of frequency of the different grades of "openness" of nostril when one parent is heterozygous and the other recessive, i. e., with closed nostril (DR × R).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Race.	Gr.		1	2	3	4	5	6	7	8	9	10
13	768	298	F2	Med. × Polish	2	1689	P.	Med.	1	3	11	9	3	1	3	...	1	...	...	...
14	768	509	F1	Do.	1	1689	P.	Do.	1	2	12	5	6	1	1	...	...	...	...	...
				Totals (53)							23	14	9	2	4	0	1	...	...	...
				Percentages							43.4	26.4	17.0	3.8	7.6	...	1.9	...	...	...

The study of the tables 45 to 54 establishes the following conclusions:

First, high nostril is dominant. This means that there is a factor that inhibits the development of the narial flap. In the absence of such a factor the flap goes on developing normally. This hypothesis is opposed to the conclusion that I reached in my report of 1906 (pp. 68, 69). I there said:

A close agreement exists between the percentage obtained in each generation and the expectation of the Mendelian theory, assuming that narrow nostril is dominant. The statistics do not, however, tell the whole story. In 36 per cent of the cases in the F₁ generation the nostril was wider than in the "narrow" ancestor. Even in the F₂ generation nearly half of the "narrow and intermediate" were of the intermediate sort. This intermediate form is evidence that dominance is imperfect and segregation is incomplete.

Table 48.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (DR × DR).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
15	802	5314	F1	Polish × Min.	3	6652	F1	Polish × Min.	4	7	1	5	5	...	...	1	...	...	3	1
16	805	5307	F1	Do.	5	4799	F1	Do.	2	7	7	7	13	3	7	1	...	2	2	1
17	852	5104	F1	Hou. × Dk. Br.	3	5969	F1	Hou. × Dk. Br.	3	6	4	11	4	2	1	1	1	...	...	...
18	805	4800	F1	Polish × Min.	3	4799	F1	Polish × Min.	2	5	10	13	9	1	2	8	...	1	2	...
19	805	5308	F1	Do.	3	4799	F1	Do.	2	5	3	7	3	2	1	...	...	...	...	...
21	759	797	F1	Houd. × Min.	3	570	F1	Houd. × Min.	2	5	2	4	2	2	...	...	...	...	...	2
22	759	797	F1	Do.	3	352	F1	Do.	1	4	...	2	2	...	...	...	...	...	1	1
23	805	4447	F1	Polish × Min.	2	4799	F1	Polish × Min.	2	4	6	5	4	...	2	...	1	1	3	...
24	805	4765	F1	Do.	2	4799	F1	Do.	2	4	5	12	4	2	1	1	2	...	2	...
25	805	4797	F1	Do.	2	4799	F1	Do.	2	4	4	2	6	...	...	...	...	1	...	...
26	805	5163	F1	Do.	2	4799	F1	Do.	2	4	7	17	13	4	1	2	2	2	1	...
27	805	5304	F1	Do.	2	4799	F1	Do.	2	4	5	9	8	...	1	...	...	...	...	...
28	852	7070	F1	Hou. × Dk. Br.	1	5969	F1	Hou. × Dk. Br.	3	4	4	11	4	2	1	1	1	...	...	...
29	759	529	F1	Houd. × Min.	2	570	F1	Houd. × Min.	2	4	2	3	...	...	...	...	...	...	...	1
30	759	529	F1	Do.	2	352	F1	Do.	2	4	1	3	...	...	...	...	...	...	...	...
31	728	174	F1	Hou. × Wh.L.	1	258	F1	Hou. × Wh.L.	2	3	2	7	2	1	1	1	1	...	...	...
32	805	4798	F1	Polish × Min.	1	4799	F1	Polish × Min.	2	3	7	10	3	2	1	2	...	4	2	...
33	805	5323	F1	Do.	1	4799	F1	Do.	2	3	17	7	2	...	...	1	...	2	1	...
				Totals (435)							92	147	88	21	22	19	10	13	17	6
				Percentages							21.2	33.8	20.2	4.8	5.0	4.4	2.3	3.0	3.9	1.4

Table 49.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (DR × DR, F₂ and later generations).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
34	763	3799	F2	Hou. × Wh. L.	6	2247	F2	Hou. × Wh. L.	2	8	...	2	2	2	2	...	1	...	...	...
35	765	84	F1	Do.	3	1794	F2	Do.	5	8	1	6	8	1	4	1	1	2	6	3
36	765	984	F2	Do.	3	1794	F2	Do.	5	8	8	3	1	2	2	1	0	2	5	...
37	802	4013	F2	Polish × Min.	4	6652	F1	Polish × Min.	4	8	6	12	9	6	...	...	...	1	1	1
38	802	3954	F3	Do.	3	6652	F1	Do.	4	7	4	12	3	2	1	...	2	6	9	1
39	802	4038	F2	Do.	3	6652	F1	Do.	4	7	3	8	4	3	2	...	1	4	1	1
40	802	4164	F2	Do.	3	6652	F1	Do.	4	7	6	8	6	2	1	1	...	2	2	2
41	812	84	F1	Hou. × Wh. L.	3	4118	F3	Hou. × Wh. L.	4	7	...	1	5	2	2	1	1	1	1	2
42	812	913	F2	Do.	3	4118	F3	Do.	4	7	10	6	6	1	...	...	...	3	2	5
43	812	4728	F3	Do.	3	4118	F3	Do.	4	7	8	5	5	1	5	2	2	2	9	2
44	812	5120	F3	Do.	3	4118	F3	Do.	4	7	1	2	2	...	1	...	...	...	1	2
45	812	5540	F3	Polish × Min.	3	4118	F3	Do.	4	7	2	5	6	1	1	...	...	...	...	...
46	763	2250	F3	Hou. × Wh. L.	5	2247	F2	Do.	2	7	4	10	2	...	...	...	...	1	0	2
47	812	4726	F2	Do.	2	4118	F3	Polish × Min.	4	6	4	6	3	...	2	1	...	2	1	3
48	812	4735	F2	Do.	2	4118	F2	Do.	4	6	2	1	1	...	...	...	...	2	1	...
49	765	1790	F3	Do.	1	1794	F2	Hou. × Wh. L.	5	6	9	14	9	1	3	0	2	0	3	...
50	802	4012	F3	Polish × Min.	1	6652	F1	Polish × Min.	4	5	5	13	11	3	2	...	1	3	1	...
51	825	2198	F3	Do.	3	3852	F3	Do.	2	5	...	...	1	3	...	...	...	...	...	1
52	728	2271	F2	Hou. × Wh. L.	3	258	F1	Hou. × Wh. L.	2	5	4	3	1	7	2	1	3	1	1	2
53	763	2700	F2	Do.	3	2247	F2	Do.	2	5	1	2	3	3	...	1	...	...	2	...
54	825	350	F1	Polish × Min.	2	3852	F3	Polish × Min.	2	4	4	13	6	4	...	...	...	3	1	3
55	825	4708	F3	Do.	2	3852	F3	Do.	2	4	4	13	7	3	...	1	1	1	2	3
56	825	5019	F2	Do.	2	3852	F3	Do.	2	4	1	1	...	...	...	...	...	1	2	2
57	825	5035	F3	Do.	2	3852	F3	Do.	2	4	4	...	3	1	1	...	...	1	1	1
58	825	5672	F3	Do.	2	3852	F3	Do.	2	4	1	3	2	...	2	...	...	1	2	1
59	728	2248	F2	Hou. × Wh. L.	2	258	F1	Hou. × Wh. L.	2	4	3	6	7	2	...	...	1	0	1	3
61	763	377	F1	Do.	1	2247	F2	Do.	2	3	20	9	14	3	6	0	2	0	2	1
				Totals (663)							115	641	127	53	39	10	8	39	57	41
				Percentages							17.4	24.7	19.2	8.0	5.9	1.5	2.7	5.9	8.6	6.2
											69.3				30.7

These earlier data were not even roughly quantitative, and it is the quantitative data that first give the key to the true relations. However, sufficient evidence for the change in the conclusion is certainly due. The evidence is found in a careful study of table 55, keeping constantly in mind this fundamental principle that the recessive condition alone in the parents can never give rise to the dominant; for the recessive condition implies entire absence of the dominant factor. But the pure dominant condition will vary in the direction of the recessive condition; such a result implies only a partial failure of the factor to develop completely; and we should not be surprised if occasionally the failure were complete. This implies no "reversal of dominance," but rather an arrested development of the factor.

Table 50.—Distribution of frequency of grades of "openness" in offspring when one parent is heterozygous and the other an original dominant (DR × D, originals).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
62	803	529	F1	Houd. × Min.	3	7522	P.	Houd.	9	12	4	2	4	1	2	...	...	2	2	1
63	803	7065	F1	Houd. × Dk. Brah.	1	7522	P.	Do.	9	10	6	11	6	4	2	1	2	6	4	1
				Totals (61)							10	13	10	5	4	1	2	8	6	2
				Percentages							16.4	21.3	16.4	8.2	6.5	1.6	3.3	13.1	9.8	3.3
											62.3				37.7

Table 51.—Distribution of frequency of grades of "openness" in offspring when one parent is heterozygous and the other an extracted dominant (DR × DD, extracted).

[Abbreviations: H = Houdan; L = Leghorn; M = Minorca; P = Polish; WL = White Leghorn.]

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
64	832	4404	F3	H × WL	4	5119	F3	H × WL	10	14	1	1	1	2	...	...	...	8	1	1
65	729	913	F2	Do.	6	936	F2	Do.	10	16	5	6	16	2	5	...	3	11	11	10
66	819	57	F1	P × M	4	1420	F2	P × M	10	14	3	2	4	...	...	1	...	3	5	1
67	832	505	F1	(H × L)L	4	5119	F3	H × WL	10	14	2	2	3	3	2	...	2	2	2	4
68	729	935	F2	H × WL	4	936	F2	Do.	10	14	3	5	4	0	3	2	5	12	15	3
69	756	2011	F2	HPMWL	4	444	F2	Do.	10	14	...	...	...	1	...	1	...	1	4	3
70	807	185	F1	P × M	4	3894	F3	P × M	9	13	4	2	...	...	...	2	1	1	2	1
71	756	1048	F2	Do.	3	1390	F2	Do.	10	13	...	...	3	...	...	...	...	...	2	...
72	762	505	...	(H × L)L	3	444	F2	H × L	10	13	1	1	3	1	1	2	2	2	3	4
73	762	2011	F3	HPML	4	2621	F2	HPML	9	13	...	1	...	...	...	...	1	1	3	1
74	813	2271	F2	H × WL	5	3904	F3	H × WL	7	12	1	5	5	2	2	1	3	2	4	9
75	820	984	F2	H × L	3	4731	F3	P × M	9	12	...	5	4	2	5	1	...	5	5	4
76	728	2272	F2	Do.	10	258	F1	H × L	2	12	2	7	9	4	4	3	2	7	7	9
77	756	1043	F2	P × M	2	1390	F2	P × M	10	12	5	5	3	2	...	...	...	3	2	2
78	762	505	...	(H × L)L	3	2621	F3	HPML	9	12	1	...	...	...	...	1	...	...	...	3
79	803	2250	F2	H × L	3	7522	P.	Houd.	9	12	...	5	2	2	4	...	...	4	9	6
80	803	2254	F2	Do.	3	7522	P.	Do.	9	12	6	6	4	1	2	1	1	3	6	3
81	769	492	F1	Do.	2	911	F2	H × L	9	11	3	6	1	1	...	2	...	...	1	...
82	807	1043	F3	P × M	2	3894	F2	P × M	9	11	9	4	2	...	3	3	...	6	6	...
83	769	2254	F2	H × L	1	911	F2	H × L	9	10	7	7	2	1	...	...	1	2	4	1
84	813	935	F2	Do.	3	3904	F3	Do.	7	10	1	2	...	4	4	3	...	7	8	1
85	813	5113	F3	Do.	3	3904	F3	Do.	7	10	4	5	5	...	1	1	1	6	8	5
86	813	5142	F3	Do.	3	3904	F3	Do.	7	10	...	2	...	...	...	...	...	1	1	3
87	813	5122	F3	Do.	2	3904	F3	Do.	7	9	...	1	2	...	1	...	...	2	2	3
88	813	7320	F3	Do.	2	3904	F3	Do.	7	9	...	6	1	...	1	...	...	2	5	2
89	813	377	F1	Do.	1	3904	F3	Do.	7	8	10	...	6	1	...	...	1	4	3	...
				Totals (641)							68	86	80	29	38	24	23	95	119	79
				Percentages							10.6	13.4	12.5	4.5	5.9	3.7	3.6	14.8	18.6	12.3
											41.0				59.0

Table 52.—Distribution of frequency of grades of "openness" in offspring when both parents are extracted dominants (extracted DD × DD).

[Abbreviations: H = Houdan; L = Leghorn; M = Minorca; P = Polish; WL = White Leghorn.]

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
91	729	2016	F2	HPLM	10	936	F2	H × L	10	20	...	...	...	...	...	...	...	4	6	5
92	729	2255	F2	H × L	10	936	F2	Do.	10	20	3	3	...	...	...	1	2	5	11	10
93	729	2269	F2	Do.	10	936	F2	Do.	10	20	...	1	...	...	...	1	...	3	9	13
94	729	2324	F2	HPLM	10	936	F2	Do.	10	20	2	3	...	...	1	1	...	5	16	7
95	756	1067	F2	P × M	10	1390	F2	P × M	10	20	...	1	3	2	1	...	...	1	1	...
96	756	1113	F2	Do.	10	1390	F2	Do.	10	20	...	...	...	...	...	...	1	4	8	4
97	762	2014	F3	HPLM	10	444	F2	H × L	10	20	...	...	...	...	...	...	...	...	1	4
98	819	1113	F2	P × M	10	1420	F2	P × M	10	20	...	...	...	...	...	...	...	2	6	2
99	819	4257	F3	Do.	10	1420	F2	Do.	10	20	...	...	2	...	...	...	...	4	4	3
100	832	4732	F3	H × L	10	5119	F3	H × L	10	20	...	...	...	...	...	...	...	2	1	...
101	832	6481	F3	Do.	10	5119	F3	Do.	10	20	...	...	...	...	...	...	...	2	5	4
102	756	369	F2	P × M	9	1390	F2	P × M	10	19	...	2	...	...	...	...	...	...	1	1
103	762	2618	F2	HPLM	9	444	F2	H × L	10	19	...	...	...	...	...	...	...	1	1	...
104	762	3776	F2	H × L	9	444	F2	Do.	10	19	...	...	...	...	...	...	...	1	1	...
105	832	5803	F3	Do.	9	5119	F3	Do.	10	19	...	...	1	1	...	...	1	6	9	6
106	807	1067	F2	P × M	10	3894	F3	P × M	9	19	...	1	1	1	2	1	2	1	4	2
107	762	2333	F3	HPLM	8	444	F2	H × L	10	18	...	...	...	...	...	...	1	2	5	4
108	762	2618	F2	Do.	9	2621	F3	HPLM	9	18	...	...	...	...	...	...	...	1	2	2
109	762	3776	F2	H × L	9	2621	F3	Do.	9	18	...	...	...	...	1	...	2	4	4	...
110	819	5674	F2	P × M	8	1420	F2	P × M	10	18	1	...	1	...	...	...	2	1	3	2
111	820	2016	F2	HPLM	9	4731	F3	Do.	9	18	...	...	...	...	1	...	1	1	4	...
112	820	2255	F2	H × L	9	4731	F3	Do.	9	18	...	...	...	...	...	...	1	2	6	5
113	820	6479	F3	Do.	9	4731	F3	Do.	9	18	...	...	1	...	2	1	2	9	12	4
114	832	2618	F2	HPLM	8	5119	F3	H × L	10	18	1	1	3	4	...	...	...	...	12	3
115	832	3776	F2	H × L	8	5119	F2	Do.	10	18	...	3	3	...	2	...	...	...	...	...
116	834	2324	F2	HPML	9	5090	F2	Do.	9	18	...	1	...	...	...	1	...	10	10	3
117	762	2333	F3	HPLM	8	2621	F3	HPLM	9	17	...	...	...	...	1	...	1	...	...	1
118	807	5075	F2	P × M	7	3894	F3	P × M	9	16	...	1	...	...	2	1	...	5	7	7
119	820	5143	F3	H × L	7	4731	F3	Do.	9	16	1	1	2	5	...	1	3	10	10	12
120	813	2272	F2	Do.	9	3904	F3	H × L	7	16	1	1	1	...	1	...	2	5	7	7
				Totals (472)							9	19	18	13	14	8	22	93	169	105
				Percentages							1.9	4.0	3.8	2.8	3.0	1.7	4.7	19.8	36.0	22.3

Table 53.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (RR × DR).

Serial No.	Pen No.	Mother.				Father.				Grade of openness in offspring.
		No.	Gen.	Races.	Grade.	No.	Gen.	Races.	Grade.	1	2	3	4	5	6	7	8	9	10
121	728	174	F1	Houd. × Legh.	1	1258	P.	Brah. × Tosa.	2	2	7	2	1	1	1	1	...	...	...
122	728	912	F2	Do.	2	258	F1	Houd. × Legh.	2	7	3	3	2	1	...	...	...	...	...
123	763	3799	F1	Min. × Houd.	6	2247	F2	Do.	2	...	2	2	2	2	...	1	...	2	...
124	802	509	F2	Polish × Min.	1	6652	F1	Polish × Min.	4	6	6	1	...	1	...	...	...	...	...
125	802	3846	F2	Do.	2	6652	F1	Do.	4	1	6	3	1	1	...	...	...	...	...
126	802	5025	F3	Do.	2	6652	F1	Do.	4	8	10	4	3	2	...	...	...	...	...
127	802	5087	F3	Do.	2	6652	F1	Do.	4	7	9	12	2	...	1	...	...	...	1
				Totals (217)						31	43	27	11	8	2	2	0	2	1
				Percentages						24.4	33.9	21.3	8.7	6.3	1.6	1.6	0	1.6	0.8

Table 54.—Distribution of frequency of grades of "openness" in offspring when both parents are extracted recessives (extracted RR × RR).

[A] Cf. Serial No. 12a.

Serial No.

Pen No.

Mother.

Father.

Total gr.

Offspring.

No.

Gen.

Races.

Grade.

No.

Gen.

Races.

Grade.

Grade 1

Grade 2

128

728

[A]912

F2

Houd. × Legh.

2

1298

F2

Houd. × Legh.

1

3

3

3

129

827

298

F2

Pol. × Min.

2

3852

F3

Do.

2

4

5

5

At the outset, then, we find (table 55) that even pure races with high nostril (Polish, Houdans), when bred together, vary much in the height of nostril (in perfection of dominance) and, in 2 per cent of the offspring, even show the typical narrow nostril (fig. B, a). On the other hand, in the narrow-nostriled races I have never obtained any such variation. The most deviation that I have seen from grade 1 is found in my strain of Dark Brahma bantams that frequently give grade 2. The variability of the high nostril, the stability of the low nostril, is prima facie evidence that the former is due to the presence of a particular factor and the latter to its absence.

Fig. B.—Polygons of frequency of grades of "openness" of nostril in offspring of various parents.
a, Both parents pure bred dominants; b, both parents extracted dominants; c, one parent heterozygous, the other a dominant; d, both parents heterozygous; e, dominant by recessive; f, heterozygous by recessive; g, heterozygous by extracted recessive; h, extracted recessives; i, heterozygous by dominant; k, both parents second generation hybrids.

Next, the heterozygotes of F₁ (table 46), may be appealed to; but they will give no critical answer. For expectation, dominance being imperfect, is that the hybrids will be intermediate, and the result will be the same whichever extreme grade is taken as dominant. The empirical mode in the distribution of the offspring is at grade 2. This implies much greater imperfection of dominance on the hypothesis that grade 10 is dominant than on the hypothesis that grade 1 is dominant; but this very fact supports the former hypothesis, since imperfection of dominance is obviously a feature of the character with which we are dealing.

The critical test is afforded by the F₂ generation (tables 48 and 49). By hypothesis, 25 per cent of the offspring are expected to be pure ("extracted") recessives, and the same number pure dominants; and also, by hypothesis, the recessives are massed at or near one grade while the dominants are variable. Now, as a matter of fact, the upper 25 per cent range over 5 to 7 grades, while the lower 25 per cent are nearly massed in grade 1 (21 per cent are so massed in one table, 17 per cent in the other). Therefore, in accordance with hypothesis we must regard the lower grade—narrow slit—as recessive. Similarly, heterozygous × low nostril (table 47) should give, on our hypothesis, 50 per cent low nostril. If that is recessive we should expect a massing of this 50 in the first two grades; if dominant a greater scattering. The former alternative is realized. Again, in the heterozygous × high nostril hybrid (table 50) the upper 50 per cent will be massed or scattered according as high nostril is recessive or dominant. Allowing for the 50 per cent heterozygotes in the progeny, the 50 per cent of high nostrils are scattered through at least 8 grades of the possible 10. High nostril is dominant. Finally, extracted high nostrils bred together produce offspring (table 52) with a great range of variability (through all grades), while extracted low nostrils (unfortunately all too few) give progeny with grades 1 and 2 (table 53; fig. B, h). Accepting, then, the general principle of the greater variability of the dominant character, we have demonstrated conclusively that high nostril, or rather the factor that determines high nostril, is dominant.

Comparing tables 45 to 54, we see that recessive parents are characterized by a low grade of nostril and they, of course, tend to produce offspring with a low grade. Similarly, dominants have a high grade and tend to produce offspring of the same sort, while heterozygous parents are of intermediate grade and their children have nostril grades that are, on the average, intermediate. Without regarding the gametic constitution, we might conclude, with Castle, that offspring inherit the grade of their parents, and consequently it would be possible to increase the grade, perhaps indefinitely, by breeding from parents with the highest grade. Considering the gametic constitution of the parents, it is obvious that such a conclusion is premature. To get an answer to the question it is necessary to find if there is, inside of any one table, among parents of the same gametic constitution, any such relation between parental and filial grades. This can be determined by calculating the correlation between the grades of parents and progeny. Such calculation I have made for table 48 with the result: index of correlation, r = 0.018 ± 0.032, which is to be interpreted as indicating that no correlation exists; and in so far the hypothesis of Castle proves not to apply in the cases of booting and doubt is thrown on the significance of his conclusion.

Finally, if we throw together the frequency distributions of all tables into one table (table 55; compare fig. B) we shall find the totals instructive. Table 55 shows that, when all results are thrown together, including hybrids of all sorts, grade 2 and grade 9 are the most frequent and grade 6 is the least frequent, the frequency gradually rising towards the extremes of the series. The same result appears in the individual series that range from grade 1 to grade 10. What is the meaning of this result? It seems to me to bear but one interpretation, namely, that there are only two centers of stability—about grades 1 and 9—and true blending of these grades, giving an intermediate condition, does not occur. Otherwise, in consequence of the repeated hybridization, the intermediate grades must be the commonest instead of the rarest. There is alternative inheritance of the nostril height.

Table 55.—Summary of tables 45 to 54.

ABSOLUTE FREQUENCIES.
Table No.	Nature of mating (parental nostril).	Nature of mating.	Grade of openness in offspring.
			1	2	3	4	5	6	7	8	9	10	Total
45	High × high	D × D	2	2	1	1	6	5	8	28	39	27	119
46	High × low	D × R	13	19	9	7	2	4	1	1	...	...	56
47	Heterozygous × low	DR × R	23	14	9	2	4	...	1	...	...	...	53
48	Heterozygous × heterozygous	DR × DR	90	140	86	20	21	18	9	13	17	6	420
49	Do.	F2(DR × DR)	117	171	129	54	40	11	19	39	57	41	678
50	Heterozygous × high	DR × D	10	13	10	5	4	1	2	8	6	2	61
51	Do.	DR × DD	71	96	73	30	39	24	23	95	119	68	638
52	Extra high × high	DD × DD	9	19	18	15	14	8	22	93	169	105	472
53	Heterozygous × extracted low	DR × RR	40	35	26	7	3	1	...	...	...	...	112
54	Extra low × low	RR × RR	8	8	...	...	...	...	...	...	...	...	16
	Totals		378	512	361	141	133	72	85	277	407	249	...
PERCENTAGES.
Table No.	Nature of mating (parental nostril).	Nature of mating.	Grade of openness in offspring.
			1	2	3	4	5	6	7	8	9	10	...
45	High × high	D × D	1.7	1.7	0.8	0.8	5.0	4.2	6.7	23.5	32.8	22.7	...
46	High × low	D × R	23.2	34.0	16.1	12.5	3.6	7.1	1.8	1.8	...	...	...
47	Heterozygous × low	DR × R	43.4	26.4	35.9	3.8	7.6	...	1.9	...	...	...	...
48	Heterozygous × heterozygous	DR × DR	21.5	33.3	20.5	4.8	5.0	4.3	2.1	3.1	4.1	1.2	...
49	Do.	F2(DR × DR)	17.3	25.2	19.0	8.0	5.9	1.6	2.8	5.8	8.4	6.1	...
50	Heterozygous × high	DR × D	16.4	21.3	16.4	8.2	6.6	1.6	3.3	13.1	9.8	3.3	...
51	Do.	DR × DD	11.1	15.1	11.4	4.7	6.1	3.8	3.6	14.9	18.7	10.7	...
52	Extracted high × high	DD × DD	1.9	4.0	3.8	3.2	3.0	1.7	4.7	19.7	35.8	22.2	...
53	Heterozygous × extracted low	DR × RR	35.8	31.3	23.2	6.3	2.7	0.9	...	...	...	...	...
54	Extracted low × low	RR × RR	50.0	50.0	...	...	...	...	...	...	...	...	...

CHAPTER VIII.
CREST.

In my report of 1906 I called attention to the nature of inheritance of the crest in the first and second generations. The result seemed simple enough on the assumption of imperfect dominance. However, in later generations difficulties appeared, one of which was referred to in a lecture given before the Washington Academy of Sciences in 1907. I stated (1907, p. 182), that "when a crested bird is crossed with a plain-headed one, and the crested hybrids are then crossed inter se, the extracted recessives of the second hybrid generation are plain-headed, to be sure, but they show a disturbance of certain feathers." This was an illustration of the statement that recessives which are supposed to come from two pure recessive gametes show in their soma traces of the dominant type. Dr. W. J. Spillman, who was present, made the suggestion that the crest is composed of two characters, T and t, instead of a simple element, and that when t alone is present the result will be the roughened short feathers on top of the head.

Further studies demonstrate the validity of this suggestion. There are in the crest two and probably three or more factors. There is a factor that determines length of the feathers and a factor that determines their erectness. There is probably also an extension factor that controls the area that the crest occupies on the head. Thus flatness of position dominates over its absence (or erectness). This is seen even in the first generation. Figs. 5, 6, 8, and 17 of my report of 1906 show this very plainly. They also show that continued growth of feather is dominant over interrupted growth. Thus in the second hybrid generation I got birds with short and erect feathers and one of these is shown in fig. 11 of the 1906 report. That shortness is recessive is proved by various matings of extracted short × short crest. Of 29 offspring none have a higher grade than 1, grade 10 being of full length. On the other hand, two parents with long feathers in the crest (grades 6 to 8) give 5 offspring of grade 1, 12 of grades 5 to 10, thus approaching the 1:3 ratio expected from two DR parents. That erectness is recessive is proved by various matings of extracted erect × erect crest. Of 25 offspring none has a lower grade than 4 (1 case) or 5 (1 case). On the other hand, two parents with extracted non-erect feathers give in 46 offspring 13 with feathers whose grade of erectness is 6 or higher and 33 with a grade of 5 or below—of these half of grade 0—close to the expected 1:3. The evidence is conclusive that there are two factors in crest that behave in Mendelian fashion—a factor determining the prolonged growth of the feather and a factor causing the feathers to lie repent.

The area of the head occupied by the crest is also variable. This was estimated in tenths for each of the parents and offspring. Two principal centers of variation appeared, at 3 and at 8, or roughly one-third and two-thirds the full area. The results, being based on estimates, are not wholly satisfactory, but so far as they go they indicate that when both parents have a crest that belongs to the lower center of variation their offspring belong chiefly if not exclusively to that center; but when they both belong to the upper center of variation a minority of the offspring belong to the lower center. Provisionally it may be concluded that extensive crest is dominant over the restricted crest or that there is an "extension factor."

CHAPTER IX.
COMB-LOP.

In races having a large single comb this is usually erect in the male, but in the female lops over to the right or left side of the head. This lop is determined before hatching; indeed, in the male it may be ascertainable only in the embryo or in the recently hatched chick. The position of the comb is permanent throughout the life of the pullet and hen and, if pressed to the opposite side, it quickly returns to its original position. At one time I entertained the hypothesis that its position was determined by the pressure of the foot against the head while the chick was still within the shell; but after finding the comb lying both to the right and to the left when in contact with the foot I abandoned this hypothesis as untenable. It seemed possible that this position is hereditary, and so data were collected to test this hypothesis. It is not always easy to decide definitely, even for the female, as to the direction of the lop; for the anterior part of the comb may lop to the right, the posterior part to the left, or vice versa. In that case one selects the larger or better defined lopping portion to designate as the lop. This is usually the posterior portion of the comb. However, such doubtful cases may be omitted from consideration here, as there are plenty of examples of well-defined lop on both sides of the head.

Table 56.

Both parents with right lop.
Pen No.	No. of mother.	No. of father.	Offspring.
			Right.	Left.
817	6188	3900	7	8
817	6406	3900	12	17
831	1011	4213	7	16
831	3040	4213	13	10
831	4219	4213	4	21
831	6602	4213	6	15
833	1310	4222	4	7
833	4361	4222	6	4
833	7519	4222	2	4
904	4714	7870	6	7
			67	109
Both parents with left lop.
841	3867	3890	3	9
841	4663	3890	9	7
903	9824	8463	6	5
			18	21
Mother left lop, father right.
831	1980	4213	9	17
904	3901	7840	4	3
904	7645	7840	6	3
			19	23
Mother left lop, father right.
903	3946	8463	2	0
903	4079	8463	7	2
903	4082	8463	11	6
			20	8
Summary.
Parents		Offspring.
		Total.	Right.	Left.
			P. ct.	P. ct.
Both with right lop		176	38	62
Both with left lop		39	46	54
Mother left lop, father right		42	45	55
Mother right lop, father left		28	71	29

From table 56 it appears, summing all cases, that there are more left-lopping offspring than right-lopping as 161 to 124 or as 56.5 per cent to 43.5 per cent and that this excess holds whether both parents are right-lopping, or both left-lopping, or the mother left and the father right. Only in the case when the mother is right-lopping is there a majority of offspring of the same sort, but here the numbers are too inconsiderable to carry much weight. Although there is not clear evidence of any sort of inheritance, it is probable that the position of the lop is not determined by a single factor, but by a complex of factors.

The conclusion that right and left conditions are not simple, alternative qualities accords with the results obtained by others. Thus Larrabee (1906) finds that the dimorphism of the optic chiasma of fishes (in some cases the right optic nerve being dorsal and in others the left) is not at all inherited, but in each generation the result is strictly due to chance. This is, perhaps, the same as my conclusion that the hereditary factors are complex. Lutz (1908) finds that in the mode of clasping the hands interdigitally the right thumb is uppermost in 73 per cent of the offspring when both parents clasp with right thumb uppermost, but in only 42 per cent of the offspring when both parents clasp with left thumb uppermost. The mode of clasping is inherited, but not in simple Mendelian fashion.

CHAPTER X.
PLUMAGE COLOR.

A. THE GAMETIC COMPOSITION OF THE VARIOUS RACES.

Plumage color, like hair color, varies greatly among domesticated animals. This diversity is, no doubt, in part due to the striking nature of color variations, but chiefly to the fact that the requisite variations are afforded in abundance. The principal color varieties, in poultry as in other domesticated animals, are melanism, xanthism, and albinism. In addition, poultry show the dominant white, or "gray" white, first recognized in poultry by Bateson and Saunders (1902), which is also found in many mammals, as, for instance, in goats, sheep, and cattle. Besides these uniform colors, we find numerous special feather-patterns, such as lacing (or edging of the feather), barring, penciling, and spangling. Also, there are special patterns in the plumage as a whole, such as wing-bar, hackle, saddle, breast, and top of head (crest). Now, all of these color characters are inherited each in its own definite fashion.

In studying the color varieties of poultry we must first of all, as in flower color (Correns, 1902), mice (Cuénot, 1903), guinea-pigs and rabbits (Castle), various plants and animals (Bateson and his pupils), recognize the existence of certain "factors." In poultry the factors that I have determined are as follows:

• C, the color factor, absence of which results in albinism.
• J, the Jungle-fowl pattern and coloration.
• N (nigrum), the supermelanic factor.
• X, the superxanthic or "buff" factor.
• W, the graying (white) factor.

We have now to consider how these factors are combined in birds of the different races.

1. WHITE.

Albinos.—These seem to be of two different origins:[9] White Cochins and white Silkies. The white Silkies that I have studied have the gametic formula cJnwx; i. e., they have the Jungle-fowl marking, but lack the "color enzyme," supermelanic coat, the graying factor, and the xanthic factor.

"Grays."—White Leghorns and their derivatives belong to this class. Its gametic formula is: CJNWx. This indicates that the race contains the color enzyme, as well as the Jungle pattern and the supermelanic coat. But all of these are rendered invisible by the graying factor W. The superxanthic factor is missing.

2. BLACK.

The uniform black birds that I have studied are of several sorts. The Black Minorca and White-faced Black Spanish have the gametic formula CJNwx. Owing to the absence of the graying factor and the presence of the color factor these appear as pigmented birds, but the supermelanic coat, N, obscures the Jungle coloration, so that the bird appears entirely black. Nevertheless the black is not of uniform quality, but just those parts of the feathers of the wing, back, hackle, saddle, and breast that are red in the Jungle fowl are of an iridescent black, while the portion that is not red in the Jungle is of a dead black.

The Black Cochin has the gametic formula CINwx. This differs from the formula of the Minorca only in this respect: the Jungle pattern is present, but not the pigmentation that is usually associated with it.

The Black Game ("Black Devil") that I used in a few experiments seemed to have the same gametic formula as the Minorca, only the supermelanic coat was less dense.

3. BUFF.

For this color I used Buff Cochins, the original buff race. The gametic formula of this race proves to be CjnwX—the Jungle-fowl pattern being absent.

B. EVIDENCE.

The evidence for the gametic interpretations of the self-colored fowl is derived from hybridizations. It will now be presented in detail.

1. SILKIE × MINORCA (OR SPANISH).
(Plates [ 3] to [6].)

By hypothesis this cross is between cJnwx and CJNwx. The first generation should give the zygotic formula CcJ₂Nnw₂x₂, or, more simply, CcJ₂Nn. This formula resembles closely that for the Minorca; but it differs in this important respect, that the coloring factor and the supermelanic factor are both heterozygous, and hence diluted.

Actually I found, as Darwin (1876) did, that the chicks of this first hybrid generation were all wholly black. In this respect they differed markedly from the chicks of the Silkie, which are pure white, and also from the chicks of the Minorca, which are prevailingly black, but have white belly and outer primaries. The white in the young chicks of Minorcas is extremely variable in amount, but never wholly absent; in time, as the bird grows older, it is replaced by black, so that the adult male and female Minorcas have a wholly black plumage. The reason for the precocious development of black pigment over the belly and primaries of the hybrid chicks is probably the presence of an extension factor (cf. Castle, 1909) derived from the Silkie. Certain it is that the ordinary Jungle pattern develops pigment on the belly and on the wings, as well as on other parts of the plumage. The hybrid chicks may be said to have the extended pigmentation dominant over interrupted pigmentation. In the adult hybrids a difference appears between the coloration of the male and female, even as Darwin pointed out. For the latter retains its uniform blackness, while the former gains red on the wing-bar, and saddle and hackle lacing ([plate 4]). Now, since all the factors present in the Minorca, and none others, are present in the hybrids, why should the male hybrids show red, and why should the males show red and not the females? The answer to the first question is, I think, clear. While the Jungle pattern of black and red is completely obscured by the undiluted N factor of the Minorca, it is only incompletely covered by the diluted, heterozygous N factor of the hybrid. Hence the red appears in greatly reduced amount, as compared with the Jungle-fowl. In the female Jungle-fowl there is little red and consequently none shows in the female hybrid. Thus the difference in the sexes of the hybrids corresponds to the sexual dimorphism of the Jungle-fowl; but the hybrids are, as indicated, very unlike the Jungle-fowl in coloration (cf. plates [ 1] and [2]).

Since segregation takes place in the gametes of these heterozygotes, 4 kinds of gametes are possible, namely, CJN, CJn, cJN, cJn. On mating heterozygotes together, zygotes of 16 types will be formed, as in table 57.

Table 57.—Zygotes in F₂ of Silkie × Minorca hybrids and their corresponding somatic colors.

C2J2N2 N	C2J2Nn N	CcJ2N2 N	CcJ2Nn N
C2J2Nn N	C2J2n2 G	CcJ2Nn N	CcJ2n2 G
CcJ2N2 N	CcJ2Nn N	c2J2N2 W	c2J2Nn W
CcJ2Nn N	CcJ2n2 G	c2J2Nn W	c2J2n2 W

Table 58.

Pen No.	Black.		White.		Game.
	Observed.	Expected.	Observed.	Expected.	Observed.	Expected.
709	119	116	55	51	31	38
804	91	89	40	39	26	29
Total.	210	205	95	90	57	67

In the foregoing table there is given after each combination a letter: N standing for black, the appearance of the soma; G standing for Game-colored, and W standing for white. No distinction is made between pure blacks and those that, while black as chicks, subsequently show some red in the male. Such a distinction was impracticable because most of the color determinations are made on the young chicks. It appears that in 16 progeny expectation is 9 black, 4 white, and 3 Game-colored. Actually 362 offspring were obtained, with the results shown in table 58. Nothing is more striking than to see the hens of this F₂ generation with evidences of the female Game pattern ([plate 6]).

Comparing observed results in the distribution of colors in the F₂ generation with expectation, it is seen that the proportions are close, and this closeness of observation with expectation is evidence for the correctness of the hypothesis.

The hypothesis may be further tested in later generations by breeding together the different sorts of individuals obtained in F₂. In pursuance of such a test I mated various pure black hens with pure black cocks and those of F₁, and, as was to have been expected, obtained families of different sorts, simply because even pure blacks have differing gametic constitutions. Thus in pen 824 I mated an extracted black cock with 3 black hens. All were apparently of the zygotic constitution C₂J₂Nn, forming gametes CJN and CJn. Mated together these should give the three black combinations C₂J₂N₂, C₂J₂Nn, C₂J₂nN, to one Game, C₂J₂n₂. Actually there were obtained 64 black and 23 Game, 66 to 22 being expectation. In another pen (pen 804) an F₁ cock was mated to various black F₂ hens. The families fall into 2 classes. The cock, of course, produced gametes CJN, CJn, cJN, cJn. With four females like him (Nos. 3902, 3908, 5431, 6043) I got: black 40, white 13, Game 14; expected, black 38, white 17, Game 13. Three females (Nos. 4715, 4716, 5099) evidently produced gametes CJN, CJn. Expectation is that blacks and Games shall be produced in the proportions of 3 to 1. Actually 30:14 were obtained where 33:11 was expected. All of these results accord closely with the hypothesis.

The whites obtained in F₂ are of 3 types, but in all alike the color factor is missing. Hence it can not reappear in the offspring, and, consequently, no colored offspring are to be expected. But, first, it must be stated that the extracted whites of the F₂ generation are not always of a pure white. Indeed, the parent Silkies are in some cases not perfectly white, but show traces of "smoke." There are different degrees of albinism; the coloring enzyme may be absent to small traces. This variability in degree of albinism is familiar to all students of albinism in man. My breeding of extracted whites was done in pen 817 and consisted of a pure white cock (No. 3900) and 2 hens. Of these 1 (No. 6046) was pure white and produced in a total of 15 only white offspring, but among those that were described as unhatched I have recorded traces of pigment in 24 per cent of the cases. The second hen (No. 3899) had black flecks in the white plumage. She had 20 offspring, of which 2 (unhatched) are recorded as having N down, 2 as "blue," and 3 others show traces of black pigment. Thus, 7 birds in 20, or 35 per cent of all, show more or less black, even as the albinic mother does. On the whole, however, omitting from present consideration the phenomenon of incomplete albinism, we may say that 2 pure albino parents produce only albinic offspring, while imperfectly albinic parents produce some imperfectly albinic offspring.

2. SILKIE × WHITE LEGHORN.

By hypothesis this cross is between cJnwx and CJNWx. The first generation should give the zygotic formula CcJ₂NnWwx₂, or, more simply, CcJ₂NnWw. This formula resembles closely that of the White Leghorn, except that the coloring and graying factors and that for supermelanism are all heterozygous and hence diluted; only the Jungle coloration remains unchanged. Actually, the first generation yielded a lot of white birds like the Leghorn, but with this difference, that, as the males became mature, they gained red on the wing-bar and to a slight extent on the lacing of the saddle. The females gained a faint blush of red on the breast. Thus red appeared, in small amount, in just those places in the respective sexes which are red in the Jungle-fowl. The explanation of its appearance that I have to suggest is that, both on account of the diluting of the supermelanic coat and of the graying factor, the red of the undiluted underlying Jungle coloration is revealed.

Since the hybrids are heterozygous in respect to 3 pairs of characters, when segregation occurs each parent produces 8 kinds of gametes, as follows: CJNW, CJNw, CJnW, CJnw, cJNW, cJNw, cJnW, cJnw. When both parents produce these 8 kinds of gametes we may expect, in 64 offspring, the proportions of the several types shown in table 59.

Table 59.—Probable frequency in 64 progeny.

Zygotic formula.	White.	White + red.	Game.	Black.
C2J2N2W2	1	...	...	...
C2J2N2Ww	2	...	...	...
C2J2N2w2	...	...	...	1
C2J2NnW2	2	...	...	...
C2J2NnWw	...	4	...	...
C2J2Nnw2	...	...	2	...
C2J2n2W2	1	...	...	...
C2J2n2Ww	...	2	...	...
C2J2n2w2	...	...	1	...
CcJ2N2W2	2	...	...	...
CcJ2N2Ww	4	...	...	...
CcJ2N2w2	...	...	...	2
CcJ2NnW2	4	...	...	...
CcJ2NnWw	...	8	...	...
CcJ2Nnw2	...	...	4	...
CcJ2n2W2	2	...	...	...
CcJ2n2Ww	...	4	...	...
CcJ2n2w2	...	...	2	...
c2J2—	16	...	...	...
Total (64)	34	18	9	3

While, if the progeny were all to survive to maturity, we might expect to get the proportions of white and of white-and-red progeny called for, yet, since the red color appears in most cases at an age after the chicks are described, it will be necessary in comparing experience with calculation to combine the first two classes as whites. We then find the proportions given in table 60.

Table 60.

Color.	In 64, calculated.	In the actual 85 individuals.
		Calculated.	Observed.
White.	52	69	68
Game.	9	12	16
Black.	3	4	1

The proportion of whites agrees closely with expectation. If this is not the case with the other two classes, the discrepancy must be attributed in part to insufficient observations and in part to the difficulties of precise classification in the early stages. The result is so close, however, as to lend strong support to our hypothesis as to the gametic constitution of the parents. Nothing is more striking, and to the unprejudiced mind more convincing, than the appearance of typically Game-colored birds in the grandchildren of wholly white parents.

3. SILKIE × BUFF COCHIN.
(Plates [7], [8].)

By hypothesis this cross is between cJnwx and CjnwX. The first generation should give the zygotic formula CcJjn₂w₂Xx, or, more simply, CcJjXx. The formula differs much from that of either parent, and the progeny themselves are no less remarkable. They have a washed-out buff color (since they are heterozygous in both C and X), and the Jungle pattern shows itself in the black tail and slightly redder buff of the wing-bar and hackles in the male. Since the hybrids are heterozygous in respect to 3 pairs of characters, when segregation occurs each parent produces 8 kinds of gametes, as follows: CJX, CJx, CjX, Cjx, cJX, cJx, cjX, cjx. In F₂ the types listed in table 61 may be expected in 64 offspring.

Table 61.—Distribution of colors, theoretic classes.—Probable frequency in 64 progeny.

Zygotic formula.	White.	Buff.	Buff + black.	Game.
C2J2X2	...	...	1	...
C2J2Xx	...	...	2	...
C2J2x2	...	...	...	1
C2JjX2	...	...	2	...
C2JjXx	...	...	4	...
C2Jjx2	...	...	...	2
C2j2X2	...	1	...	...
C2j2Xx	...	2	...	...
C2j2x2	1	...	...	...
CcJ2X2	...	...	2	...
CcJ2Xx	...	...	4	...
CcJ2x2	...	...	...	2
CcJjX2	...	...	4	...
CcJjXx	...	...	8	...
CcJjx2	...	...	...	4
Ccj2x2	...	2	...	...
Ccj2Xx	...	4	...	...
Ccj2x2	2	...	...	...
c2—	16	...	...	...
Total	19	9	27	9

The classification here employed can not be used in detail in comparing observed results with expectation, for the distinction between buff and buff-and-black appears only in chicks that have acquired the permanent plumage. Consequently it will be found necessary to combine these two classes into one and then make the comparison—as is done in table 62.

Table 62.—Distribution of colors, combined classes.

Color.	In 64, calculated.	In the actual 58 individuals.
		Calculated.	Observed.
Buff (and black).	36	33	34
White.	19	17	17
Game.	9	8	7
Total.	64	58	58

The correspondence is certainly close. The hypothesis of factors thus receives additional support and the variability of the offspring in the second hybrid generation is sufficiently explained.

4. WHITE LEGHORN × BLACK MINORCA.

As we have already seen, the gametic formula of the White Leghorn is CJNWx and that of the Minorca is CJNwx, so that the F₁ generation has the zygotic formula C₂J₂N₂Wwx₂ or, more simply, C₂J₂N₂Ww. These heterozygotes are white because of the graying factor, but, as this factor is diluted, some black shows, particularly in the females. In F₂, on account of there being only 1 heterozygous factor, only 3 kinds of zygotes are formed, C₂J₂N₂W₂, C₂J₂N₂Ww, and C₂J₂N₂w₂, in the proportions 1: 2: 1. Since not only offspring homozygous in W, but also all male heterozygotes, are white and many female heterozygotes are late in revealing any pigment, it is necessary to consider together individuals homozygous and heterozygous in W. Consequently we may expect 75 per cent of the offspring to show white or white-black-speckled plumage, and 25 per cent black or black and white like the young Minorca. Actually, in 154 offspring (pen 633) I obtained 116 white + white-black + blue, and 38 black with more or less white and including 4 barred, of which more later. Expectation is 115.5 and 38.5, respectively.

In another experiment I crossed the F₁ hybrids on a pure White Leghorn and got 41 offspring, all white except 1 that showed some black specks. All results thus accord with hypothesis.

5. WHITE LEGHORN × BUFF COCHIN.
([Plate 9].)

These two races afford the gametic formulæ CJNWx and CjnwX, respectively. The F₁ hybrids consequently have the zygotic formula C₂JjNnWwXx. Such hybrids are heterozygous in all factors except C. Such complex heterozygotism, combined with the well-known sex differences in color of heterozygotes, leads to a very great diversity of the offspring. As a matter of fact I found, as Hurst did, that the young were sometimes quite white, sometimes white and buff, and sometimes showed also a little black. Since there are 4 heterozygous characters, there are 256 possible combinations of them, which reduce to 81 different kinds of combinations. Owing to the ambiguous nature of the soma in many of the heterozygotes and to the relatively small number of offspring, it is useless to compare theoretical and observed distributions of plumage colors in the somas. Suffice it to say that white, buff, black, and Game-colored chicks all appeared in the F₂ generation, as well as some with a mixture of colors, as called for by the hypothesis. White, due to the powerful graying factor, was the commonest color, buff and black were about equally common, and each about one-third as abundant as white, while Games, due to the hypostatic J factor, were about one-third as common as buff. All this, again, is explicable upon our hypothesis and upon none other so far proposed. In mating the F₂ generation with each other or with the White Leghorn the result must vary with the gametic output of the hybrid, which is obviously very different in different cases. A hen, of a light buff color spangled with white spots and having a black tail, presumably formed gametes CJnWX, CJnwX, CJNWX, CJNwX. Mated with the White Leghorn, CJNWx, she produced 8 pure whites, 4 whites with some black and red, 2 buff and white, and 3 black with trace of white. Expectation in 16 offspring would be about 4 pure whites, 4 white mixed with pigment, 4 buffs with white (and black?), and 4 blacks mixed with other colors. This is merely an illustration of the way the confused combinations of colors become intelligible, and even necessary on the factor hypothesis.

6. BLACK COCHIN × BUFF COCHIN.
([Plate 10].)

The factors involved in this cross seem to be CINx for the Black Cochin (in which I stands for the Jungle pattern without any associated color factor) and CjnX for the Buff Cochin, as before. The F₁ generation has the zygotic composition C₂IjNnXx, and the females are all black, except for a variable amount of red on the hackle, and the males are black and red, like Games. The F₂ generation is remarkable. Since 3 factors are heterozygous, there are 64 possible combinations and 27 differing ones. In table 63 is given a list of these different combinations and of the probable associated somatic colors. The prefixed number indicates the frequency of each combination.

Table 63.

1 C2I2N2X2 Black.	2 C2IiN2X2 Black.	1 C2i2N2X2 Black.
2 C2I2N2Xx Black.	4 C2IiN2Xx Black.	2 C2i2N2Xx Black.
1 C2I2N2x2 Black.	2 C2IiN2x2 Black.	1 C2i2N2x2 Black.
2 C2I2NnX2 Black and red.	4 C2IiNnX2 Black and red.	2 C2i2NnX2 Black and red.
4 C2I2NnXx Black.	8 C2IiNnXx Black.	4 C2i2NnXx Black.
2 C2I2Nnx2 Black.	4 C2IiNnx2 Black.	2 C2i2Nnx2 Black.
1 C2I2n2X2 Buff.	2 C2Iin2X2 Buff.	1 C2i2n2X2 Buff.
2 C2I2n2Xx Buff.	4 C2Iin2Xx Buff.	2 C2i2n2Xx Buff.
1 C2I2n2x2 White.	2 C2Iin2x2 White.	1 C2i2n2x2 White.

Uniting the blacks and black-and-reds (since red appears only in one sex and often not until late in life) we find the following relation between the calculated and the observed proportions in 86 offspring: Calculated, black 65, buff 16, white 5; observed, black 61, buff 17, white 8.

In still another pen (848) the F₂ hybrids were mated to a Buff Cochin. Only 21 chicks were raised. Expectation is, black 10.4, buff 5.2, white 5.2. Actually there were obtained, black 7, buff 10, white 4. Half of the calculated blacks are really heterozygous in both black and buff; so expectation is a little uncertain, and probably should be given as something under 10.4. Also, on account of small numbers, a close agreement is not to be expected; but calculation and observation are at least of the same order.

CHAPTER XI.
INHERITANCE OF BLUE COLOR, SPANGLING, AND BARRING.

A. BLUE COLOR.

Color-patterns are generalized, like the barring, spangling, and "blueing"; or localized, like the wing-bar or hackle and saddle lacing. We have to consider at present the method of inheritance of the former of these kinds of color patterns. As is well known (Bateson, Saunders, and Punnett, 1902, 1903), the Blue or Andalusian fowl is a heterozygote and, as such, produces white gametes and also black gametes.[10] The "blue" is, indeed, a fine mosaic of white and black. The barbules of a blue feather are seen to be finely barred with alternating pigmented and unpigmented zones. The pigment consists of the ordinary melanic granules of a dark sepia color.

My original blues arose (in pen 502) from a White Leghorn hen B (recognized as heterozygous but of unknown origin), mated to a black Minorca. These blues are referred to in my 1906 report. They were both females and were mated (in pen 636) to a white cock (No. 340) similarly derived. Of 49 offspring, 11, or over 22 per cent, were black and 78 per cent either pure white (35 per cent of all), white with black specks (22.5 per cent) or white-and-black mosaic, i. e., blue (20.4 per cent), but the latter were very variable in the quality of the blue. Let us designate the whitening factor of the White Leghorn by W (its absence w, resulting in black) and the blueing by M (its absence by m). Then, assuming that the blue females produce germ-cells MW, Mw, mW, mw, in equal numbers, and that the white male produces the same, we may expect in 16 F₂ offspring the combinations shown in table 64.

Table 64.—Combinations in zygotes of the second hybrid generation of the blue strain.

M2W2 1 white.	MmW2 2 white.	m2W2 1 white.
M2Ww 2 blue.	MmWw 4 white.	m2Ww 2 white.
M2W2 1 black.	Mmw2 2 black.	m2w2 1 black.
Totals: White ten-sixteenths; black four-sixteenths; blue two-sixteenths.

The relation between the calculated and the actual percentages is as follows:

• White + black specks in females: calculated, 62.5; actual, 57.5.
• Black: calculated, 25; actual, 22.1.
• Blue: calculated, 12.5; actual, 20.4.

That the agreement is not closer must be attributed to the fact of small numbers and the premature death of many of the chicks, in consequence of which their adult plumage colors were not fully revealed. Also, many "blue" chicks produce white adults with black specks in the plumage.

It is to be observed that this explanation calls for a special mosaic (blueing) factor, but this mosaic factor brings about a blue plumage only when the "white" factor is diluted, i. e., heterozygous.

In the next generation (pen 733) I mated 2 blues together. This mating is generally regarded as a unifactorial one (producing gametes WM, wM) and to give in every 4 offspring 1 black, 2 blue, and 1 white. I obtained the expected 50 per cent of blues, but always an excess of blacks and a deficiency of whites (49:35:16, respectively). This result is doubtless due to the accident that a large proportion of the chicks were described young, for it appears from my records that some blues become white when older and some "blacks" are certainly blue-blacks. The deficiency of whites becomes an excess of whites in the adult stage. The whites obtained from the blues are usually, but not always, splashed with black spots.

B. SPANGLING.

As is well known, hybrids between black fowl and White Leghorns are usually white with black patches in the females, while their brothers are mostly entirely white. This "spangled" condition is a heterozygous one just as truly as the "blue" condition is. When a splashed hen is mated to her white brother a certain proportion of the offspring are splashed again, i. e., one-half of 50 per cent or 25 per cent, that being the proportion of heterozygous females. Actually in 150 offspring 19.4 per cent were splashed and 18.6 per cent black, while 62 per cent were recorded (largely from unhatched chicks) as pure white. The splashing reappears in about the expected proportion of cases. In my pen 633 I take the spangled females to form gametes WS, Ws, wS, ws, while the male seems to form gametes Ws, ws; S being the spangling factor. Then [♀ WS, Ws, wS, ws] × [♂ Ws, ws] gives the combinations shown in table 65.

Table 65.—Combinations in zygotes of the second hybrid generation of the spangled strain.

Zygotic formulæ.	Male.	Female.	Both sexes.
W2Ss	White.	Spangled.
W2s2	White.	White.
2WwSs	White, spangled.	Spangled.
2Wws2	White.	White.
w2Ss	Black.	Black.
w2s2	Black.	Black.
Total patterns in progeny:
White.	Five-eighths.	Three-eighths.	Eight-sixteenths.
Spangled.	One-eighth.	Three-eighths.	Four-sixteenths.
Black.	Two-eighths.	Four-sixteenths.	Do.

This analysis indicates that we should occasionally see a spangled male, and this expectation is realized. Thus No. 1250 ♂ is an F₂ out of White Leghorn A and the Rose-Combed Black Minorca No. 9. He is white with black spots covering about 10 per cent of the plumage, and No. 4222 ♂ of similar origin has much black on his chiefly white plumage. When they are mated to spangled hens of similar origin with themselves (pen 775), whites, blacks, and spotted, spangled, and blues occur in the proportions of 1, 17, and 12, respectively. Here again there is a deficiency of whites in the birds as described, a deficiency again probably due to immaturity.

Of the mottled condition all degrees are found, from white splashed with black to black with white spots; also, blue is very common in the offspring of two mottled birds. The relation of these patterns is very complex and much time would be required for their complete analysis, but it seems certain that there is a spangling or mottling factor, but that, as in canaries, guinea-pigs, and rats, the precise pattern is not inherited. There are, to be sure, in poultry, so called races of spangled birds with well-defined patterns, such as the spangled Polish, spangled Hamburgs, and so forth, but it is the experience of breeders that they do not reproduce their patterns closely. The prize-winning birds—those which conform to the breeder's ideals—are only a small proportion of each family of offspring. For instance, the Ancona type of plumage, which is black, each feather tipped with white, has to be carefully sought for in the progeny of each Ancona pen. The same is true of the Silver Spangled and Golden Spangled Hamburgs. There is little true spangling in the first plumage; the darker chicks prove the best; that is, there is the same tendency to grow whiter with age that I have noted above. And, finally, only a few birds in any flock are even fairly good show birds.

C. BARRING.

The presence of bands of black running at intervals across the otherwise white feather is a condition found in many types of poultry as well as various wild birds. It has become a fixed character in the Barred Plymouth Rock, which derived it in turn from the barred Dominique, whose barring was probably derived from the Cuckoo birds of England. Barring is also said to result from some crosses between white and black birds.

In my breedings barred birds have arisen several times:

(1) White Cochin × Tosa.—This case was referred to in my earlier report.[11] In the first generation of hybrids all males were barred. In the second hybrid generation I got 15 chicks that were white or nearly so, 25 with the Game color, and 16 barred. Remembering that only the males are barred and that the young heterozygous females are classed with Games, it appears that the barring is a heterozygous condition, occurring actually or potentially in about 50 per cent of the second hybrid generation and that, the whites and some of the Games are extracted types. This conclusion is confirmed by further breeding. In pen 663 I bred 2 extracted white hens of Cochin-Tosa origin to a white cock and got 12 chicks, of which all were white, except that 3 showed a trace of reddish color. From the extracted Games bred together I got 36 chicks, all Games. In the case of this cross, consequently, barring is clearly heterozygous and confined to the male sex.[12]

(2) White Leghorn Bantam × Dark Brahma.—This cross was referred to in my report of 1906. From the table given there it appears that I got 5 barred fowl in F₁ out of a total of 51. In pen 701 I attempted to see if I could fix this barring. I used the best barred cock of the F₂ generation and the best barred hens of F₁ or F₂. The result was as shown in table 66.

Table 66.—Distribution of color in F₂ or F₂ hybrids of the barred strain.
[Abbreviations: W.L. = White Leghorn; Dk.Br. = Dark Brahma.]

[A] Including 1 blue.						[B] Including 2 blue.
Mother.				Father.				Offspring.
No.	Gen.	Races.	Color.	No.	Gen.	Races.	Color.	White.	Black.	Dark Brah.	Barred.
721	F1	W.L. × Dk.Br.	Dark barred.	1898	F2	W.L. × Dk.Br.	Barred.	...	5	7	5
894	F2	Do.	Well barred.	1898	F2	Do.	Do.	...	9	3	[A]10
965	F2	Do.	Medium barred.	1898	F2	Do.	Do.	2	16	4	8
1335	F2	Do.	Dark barred.	1898	F2	Do.	Do.	1	14	1	2
1772	F2	Do.	Poorly barred.	1898	F2	Do.	Do.	...	4	7	[B]5
1915	F2	Do.	Fairly barred.	1898	F2	Do.	Do.	...	10	4	5
2576	F2	Do.	Do.	1898	F2	Do.	Do.	...	9	11	3
		Totals (145)						3	67	37	38
		Percentages						2.1	46.2	25.5	26.2

This result suggests the interpretation that one of the parents, probably the male, contains both heterozygous black and barring, while the other parent lacks the supermelanic coat and has homozygous barring. Then of the offspring half will be barred and half will be black and, consequently (since only the non-black show their barring), one-fourth will appear barred, one-fourth will appear of the Dark Brahma type, and half will be pure black or have the pattern obscured by the supermelanic coat.

(3) White Leghorn Bantam × Black Cochin.—In still another experiment (pen 511) I crossed a White Leghorn bantam and a Black Cochin as described in my report of 1906. Of 24 hybrids that developed, 10 were white or nearly so, 7 were black, and 7 were barred black and white. The White Leghorn was heterozygous in white (half of the offspring being not white) and heterozygous to barring. In pen 650 the barred birds were mated together with results as given in table 67.

On the assumption that the zygotic formula of both hens and cocks is BbN₂Ww (compatible with a barred plumage) we get four-sixteenths of the offspring white, three-sixteenths mottled or barred and nine-sixteenths black or Game, thus approximating the observed result; i.e., 21, 16, 47 as compared with 23, 21, 40. The result supports the hypothesis of a barring factor, B.

Table 67.—Distribution of color in offspring of barred White Leghorn × Black Cochin hybrids.

Mother.				Father.				Offspring.
No.	Gen.	Races.	Color.	No.	Gen.	Races.	Color.	Wh.	Spangled, barred and blue.	Black or Game.
263	F1	Bl. Coch. × Wh. Legh.	Barred.	265	F2	Bl. Coch. × Wh. Legh.	Barred.	8	8	16
361	F1	Do.	Do.	265	F2	Do.	Do.	7	4	15
364	F1	Do.	Do.	265	F2	Do.	Do.	8	9	9
Total.								23	21	40

[84]

CHAPTER XII.
GENERAL DISCUSSION.

A. RELATION OF HEREDITY AND ONTOGENY.

In studying heredity our attention must often be focused on the ontogenesis of the different characters, and we are sometimes inclined to regard the adult character as the product of the course of ontogenesis. But this is a superficial way of looking at things; the determiners of all characters are in the germ-plasm and together they direct the development of one part after another in orderly succession; a modernized form of the pre-formation doctrine seems logically necessary.

What do we know of the processes that take place in bringing the fertilized egg, freighted with its specific heredity, to its destination—the adult form? Modern embryological and cytological studies give us an insight into many of them. First of all, the egg has a certain organization that foreshadows something of its fate. Then cell-divisions begin, at first synchronous, but later becoming accelerated here and retarded there. Eventually (especially among animals) these cells become arranged into a membrane whose unequal growth in limited areas produces foldings. The folding of membranes, their stretching, local thickenings, or thinnings are largely the result of local inhibitions of water. Sometimes movements of individual cells occur out of the membranes into and through cavities or solid yolk-masses, and by the aggregation of such cells massive organs are sometimes formed. Local absorption of tissues already established may be effected in later life by such migratory cells. Membranes once established may form pockets or linear folds, as in gastrulation and gland formation; they may become perforated; two membranes may fuse along areas or lines and a perforation may even occur at the region of fusion. Linear strands or tubules may grow out, making connections, as nerves do, with distant organs; tubes may unite to form a network, or split lengthwise. Finally, membranes and masses undergo vacuolization, or masses may split apart or fuse together. Thus in the ontogeny that is proceeding under the control of heredity all is motion and change.

What are the factors that control all these movements—for these are the true factors of heredity? We do not know much about them, but we know some things. We know that cell-divisions occur at particular times and places under the influence of preceding division planes; but their normal occurrence may be interfered with by an abnormal chemical condition of the environment.

We have reason for concluding that each developmental process is a "response"—a reaction of the living, streaming protoplasm to changing environment. The nature of the response to any stimulus probably depends on the chemical constitution of the protoplasm—and this is hereditary. In an important sense heredity is the control of ontogeny.

The specific characteristics are mostly those that appear late in ontogeny. The integumentary folds over the nasal bones of the chick appear on or about the tenth day. At that time it can be ascertained whether the comb is median, or multiple, or Y-shaped, or cup-shaped, or consists of 2 papillæ. In the case of the single-comb the fold is linear and single; in the case of the pea-comb, linear and triple; in the case of the rose-comb, quintuple or irregularly wrinkled over the whole area; in the case of the Polish-comb, there is a pair of "pocket folds." In the single-combed fowl the single linear fold grows quickly to a great height and very thin, while in the pea-comb, with its additional pair of wrinkles, the median element is not so high as in typical single-combed races; in the pea-comb there is an additional folding stimulus and a reduced growth stimulus. In the heterozygote both stimuli are weakened; the lateral folds are usually much reduced—"are hard to make out," as I stated in 1906 (p. 35); and the factor that determines the continued growth (elevation) of the fold is weakened, so that the pea-comb—although "abnormally high" (1906, p. 35, figs. 20 and 21)—is not nearly as high as the single-comb of the Minorca (1906, fig. 4).

Two results are evident: first, each character in the heterozygous condition is reduced, and, second, each is much more variable than in the homozygous condition. Why is the character reduced? If the reaction to continued growth of the fold is strong in one race and weak in the other, then in the heterozygote that reaction, whatever its nature, is reduced. Why is the reduction in the response so variable? There is a variation in the irritability or other growing factor of the embryonic material that is destined to form the fold. Even Minorcas vary in the growth of the comb, and so do the Dark Brahmas. Let G be a constant element of the growth factor of the Minorca's comb; then G + a or G - a will indicate its variants. Let g be the growth factor of the Brahma's comb, and g + a and g - a its variants. Then the hybrids of these two races may be of the following types: Gg, Gg + a, Gg - a, Gg + 2a, Gg - 2a. This gives 5 varying conditions instead of 3 and greater extremes of variation.

In the foregoing case I have assumed that the positive character is that of increased growth in the Minorca; but the positive character may be an inhibition to indefinite growth of the pea-comb. Heredity may be conceived of as exerting at all points a control on developmental processes—sometimes initiating and continuing this; but often, on the other hand, slowing down or wholly inhibiting that. The inhibition of a process is quite as positive a function of heredity as its initiation. The hair of a young rabbit grows until it attains a certain length and then the growth ceases. The growing character is a youthful, embryonic one; the new character is the stoppage of growth. Similarly the young feathers of birds grow continuously until something intervenes that stops the growth and dries up the sheath. Now, in Angora rabbits and long-tailed fowl the epidermal organ continues its embryonic growth indefinitely; the something that intervenes to stop growth is absent. There is no reason for regarding the long hair or long feather as a positive condition and short hair or feather as due to its absence.

Again, Mediterranean fowl have non-feathered shanks; but in Asiatics the feet are feathered like the rest of the body (except the soles and face). It has been assumed that boot is an additional character and should be dominant over absence of boot. But, on the other hand, we may well think of the capacity of producing feathers as general to the skin. From this point of view the real question is, what prevents feather production on the eyelids, comb, wattles, and shank? It seems equally probable that there is an inhibitor of feather-growth for these few areas as that every conceivable area of the body has its special stimulus factor for feather development; or even as that there is such a factor to each separate feather-tract. In the Minorca, then, the inhibitor of boot is present; in the Silkie a weak heterozygous inhibition appears; but in the Dark Brahma there is no inhibitor and feathers extend down from the heel over the whole of front and sides of the foot and even on the upper surface of the toes—just as they do over the anterior appendages.

The case of the rumpless fowl is important in relation to the hypothesis of inhibitors. Either tail-production depends on a special factor TT, which is diluted, as Tt, in the heterozygote; or else there is a tail inhibitor, II, which is diluted, as Ii, in the heterozygote. In F₂ we expect, on the one hypothesis, 25 per cent tt, giving no tail, and 25 per cent TT, giving tail; on the other hypothesis 25 per cent ii, giving tail, and 25 per cent II, giving no tail. Actually we get all tailed in some cases; in others 25 per cent with no tail. Which hypothesis best fits the facts? Which is the more probable—that the 25 per cent recessive no-tail should produce a tail (as it were, out of nothing) or that the 25 per cent dominant tail inhibitor should be ineffective, permitting the development of a tail? It is clear that the ontogenetic failure of an inhibitor is easier to understand than the development of a character that is not represented at all in the germ-plasm. This matter is treated in another connection in the next section. But the present point is that it is equally in accord with the facts to regard heredity as initiating and inhibiting processes. If, indeed, processes were not regularly inhibited, they must, when once started, go on indefinitely, as do the hairs of Angora goats and wonder-horses.

As we have seen, ontogeny is not completed at hatching or birth. Many characters are at that time undeveloped. Hence, not infrequently the recessive condition is at first seen and is only later replaced by the dominant condition. The reverse sequence will rarely be followed, because development rarely, except in cases of degeneration, moves backward. One of the familiar cases of this sort is human hair-color. In youth this is frequently flaxen, later it becomes light brown, and eventually it may become dark brown. Darwin gives a number of examples in his Chapter XII of Animals and Plants under Domestication. To these I may add some from my own experience. The hybrids between white and gray Java sparrows are at first light and later become of a slaty gray like the dark parent. Many black fowl gain white feathers as they grow older, and every fancier knows that birds with complex white-and-black patterns can usually be "exhibited" only once, on account of loss of "standard" coloration late in life. In these cases the advanced condition in the series of melanic colors appears only late in ontogeny.[13] Similarly Lang (1908, p. 54) finds that in snail hybrids often the young shells have the recessive yellow color, only later in life showing the dominant red color. This is, of course, no reversal of dominance in ontogeny, but mere ontogenesis of pigmentation. So in general, since the recessive condition is absence of the character or its low stage of development and the dominant condition is presence of the full character, the individual in ontogenesis may exhibit in succession the recessive and then the dominant character, but not in the reverse order.

B. DOMINANCE AND RECESSIVENESS.

If segregation is the cornerstone of modern studies in heredity, dominance forms an important part, at least, of the foundation. In any case, a critical examination of dominance is now required; the more so since its significance and value have often been doubted.

First, how is a dominant character to be defined? It has been defined both on the basis of visible results in mating and on the basis of its essential nature. On the basis of visible results in hybridizing dominant characters may be defined as Mendel (1866, p. 11) defined them: "jene Merkmale, welche ganz oder fast unverändert in die Hybride-Verbindung übergehen." Bateson's translation (1902, p. 49) renders this passage: "those characters which are transmitted entire, or almost unchanged in the hybridization."

On the basis of the essential nature of the dominant character there has obtained a great diversity of definitions. Thus de Vries (1900, p. 85) suggested that the "systematically higher" character is the dominating one, and, again (1902, pp. 33, 145), that the dominant character is the phylo-genetically older one. Many have suggested that it is the positive or present character that dominates over the negative, latent or absent. This last idea has become the prevailing one and its history is worth summarizing.

As early as 1902, Correns used as Mendelian pairs, presence of coloring material and absence; also modification into yellow and no modification. In 1905, he extended somewhat this use of present and absent characters, k (keine) preceding the symbol of a character as a negative. Still he did not pretend to generalize the relation of dominance and recessiveness to be that of presence and absence. In 1903 (p. 146) de Vries stated that in very many cases Mendel's law held when one quality is active and the other latent, and that the active quality is dominant. His illustrations show that by activity he meant essentially presence, by latency absence from the visible soma. Bateson's third report (1906) applies presence and absence to several additional cases, and, at the International Genetics Conference of that year, Hurst developed the presence-and-absence hypothesis, favoring the view that the factor for absence is nothing at all, but finding that certain cases, such as Angora coat, offer a difficulty. At the same meeting I suggested that "a variation * * * that is due to abbreviation of the ontogenetic process, which depends on something having dropped out, will be recessive," a progressive variation dominant; and in 1908 I expressed the conclusion that "dominance in heredity appears when a stronger determiner meets a weaker determiner in the germ. The extreme case is that in which a strong determiner meets a determiner so weak as to be practically absent, as when a red flower is crossed with white." I suggested that in some cases of recessiveness of an apparent advanced condition, like Angora hair, the dominant factor is an inhibitor. In the last year or two the presence-and-absence theory has gained wide acceptance, but I still think the cases where there is dominance of the advanced condition over the less advanced—of the quantitatively well-developed over the quantitatively less well-developed—have not been sufficiently considered. In human hair-color any other hypothesis demands that there are many units in the higher grades of pigmentation and fewer in the lower grades and that the presence of the surplus factor in any other higher grade dominates over its absence in the next lower grade; but there is no evidence in human hair-color of distinct, discontinuous units in the common yellow-brown series. And, in ontogeny, the different grades of color form a continuous series whose development proceeds throughout early life and may even be stimulated to an advanced stage of darkening by disease. The cessation of color development may take place at any point, and this seems incompatible with the theory of unit-characters for the different grades of human hair-color. In the present paper, on the other hand, the characters dealt with are mostly unit-characters and their quantitative variations mostly heterozygotic. Even the case of the Silkie boot ([table 31], C) referred to in an earlier paper[14] as illustrating recessiveness of the less advanced condition proves, on further analysis, to be a case of heterozygotism. It seems highly probable that the future will show that many more advanced or progressive conditions are really due to one or more unit-characters not present in the less advanced condition. In that case it will appear that there is perfect accord in the two statements that the progressive condition and the "present" factor are dominant.

The definition of dominance on the ground of results meets at the outset with a difficulty the germ of which is observable in Mendel's cautious statement "ganz oder fast unverändert." Even Mendel observed that the hybrids between white-flowered and purple-red flowered peas have flowers less intensely colored than the darker parent. The experiments of the last seven years have shown that the "dominant" character is often very greatly changed—indeed, in extreme cases a blending of characters may occur—in the first generation. Correns (1900 b, p. 110) very early stated that in a certain set of crosses between good species the hybrids showed the character of both parents, only reduced, but in varying degrees. Bateson and Saunders (1902, p. 23) found in crossing two forms of Datura that—

Although the offspring resulting from a cross between any two of the forms employed are usually indistinguishable from the type which is dominant as regards the particular character crossed, yet in other cases the intensity of a dominant character may be more or less diminished either in particular individuals or in particular parts of one individual. In Tatula-Stramonium cross-breds the corolla is often paler in color than that of the dominant parent (as has already been noticed by Naudin), but even in the palest specimens the deep blue color of the unopened anthers leaves no doubt as to the presence of the dominant color element. * * * The occurrence of intermediate forms was also occasionally noticeable in the fruits. Among the large number of capsules examined, there were some of the mosaic type, in which part of the capsule was prickly and the remainder smooth, while others, suggesting a blend, were more or less prickly all over, but the prickles were much reduced in size, and often formed mere tubercles.

Bateson and Saunders further showed (1902, p. 123) that in the case of comb and extra-toe in poultry "the cross-bred may show some blending and * * * the intensity of the dominant character is often considerably reduced."

Correns (1905, p. 9) pointed out that there was known, even at that time, a complete series of cases at one extreme of which one determiner completely hindered the appearance of the other, while at the opposite end of the series the hybrid showed an intermediate condition, both determiners appearing with equal strength.

The following year, in my first report on Inheritance in Poultry, I laid great stress on the imperfection of dominance, and this phenomenon has become more striking and clear in the subsequent years, until in the present paper it is recognized as the key to the explanation of many apparently anomalous types of heredity.

The first case in the present work in which imperfection of dominance is considered is that of the hybrids between I and oo comb. Here median comb is mated with no-median. Each somatic cell of the hybrid—at least in the comb region—has only half the full determiner for median comb. The determiner is weakened, and so the median comb is imperfectly developed, namely, at the anterior end of its proper territory. The weakening varies much in degree in the heterozygote. The median comb may be reduced to 70 per cent of its normal length or it may not develop at all.

The second case of imperfection of dominance is that of polydactylism. Extra-toe mated to normal gives extra-toe in 73 per cent only of the offspring in the case of the Houdans. Any trace of 6 toes (on one or both feet) is found in only 12 per cent of the hybrid offspring from a 6-toed Silkie parent. Certainly dominance here is very like blending.

The third case of imperfection of dominance is that of syndactylism. No syndactyls were noticed in F₁. My first conclusion was that syndactylism is recessive; but later studies have shown that it is dominant and that all matings of two syndactyl parents yield about 56 per cent syndactyl offspring.

Rumplessness gives an illustration of how dominance may be so weak as to be absent altogether; so that from F₁ alone the erroneous conclusion is drawn that it is recessive; indeed, in one strain, only faint traces of the character made their appearance in successive generations.

Finally, winglessness is a character which appears not to be inherited at all. Nevertheless our experience with rumplessness leads us to suspect that winglessness also is an impotently dominant character.

Looking at the matter frankly and without prejudice, the question must be answered: Has not the whole hypothesis of dominance become reductio ad absurdum? What visible criterion of dominance remains, where dominance fails completely? All the usual statistical landmarks of proportional appearance in successive generations being lost, can one properly speak of dominance and recessiveness at all?

Amid the general ruin of criteria, however, one means of detecting dominance remains. That extracted character which in F₂ or subsequent generations shows in homologous[15] matings in some families a wide range of variability is dominant, while that extracted character which constantly, in all homologous matings, shows no or very little variation is recessive.

The reason for this difference in the inheritableness of the two conditions is easy to understand on the principles enumerated in the last section. A positive character has a real ontogeny. But, as we have seen, the development of any character may be interrupted at any stage. Most aberrations among organisms are due to a retardation or failure of normal development. In human affairs we recognize this tendency in the terms "degenerates" and "defectives" (constituting from 2 to 4 per cent of the population). Indeed, there are few persons who are not defective in some physical or psychical character. In cases where the commonest form of abnormality is due to a development in excess it seems probable that a normal restraining or inhibiting factor is defective or absent. On page 88 I tried to show how common in ontogeny such restraining and inhibiting factors are. Since ontogenetic processes are so often cut short by external conditions, we can understand the variability in the degree of development of positive characters.

On the other hand, whenever the fundamental hereditary stimulus or the material for a character is absent from the germ-plasm of both parents, then it can appear in none of the offspring; they will be practically invariable in respect to this condition. Only the ontogenetic fluctuations of other real characters may influence the defect. Consequently the absent state reproduces itself, the "recessive breeds true."

The considerations here presented bear upon the hypothesis of change of dominance. Bateson and Punnett (1905, p. 114) say of poultry: "The normal foot, though commonly recessive, may sometimes dominate the extra-toe character." This idea of occasional change in dominance has been expressed more than once in the literature. I think the phrase an unfortunate one. In my earlier report[16] I urged that a characteristic that is anywhere dominant is so without regard to race or species involved. If this is so it is clearly improbable that it should vary from individual to individual, or in the same individual at different times. Rather in view of the imperfection of dominance we should say that a dominant character sometimes fails to develop, in which case it is absent from the progeny; that is all. It is particularly apt to fail of development when dilute—heterozygous.

C. POTENCY.

Perhaps an apology is needed for introducing the much-abused word "potency"; but there is hardly another that can be so readily adapted to the precise definition I desire to give to it. The potency of a character may be defined as the capacity of its germinal determiner to complete its entire ontogeny. If we think of every character as being represented in the germ by a determiner, then we must recognize the fact that this determiner may sometimes develop fully, sometimes imperfectly, and sometimes not at all. When such a failure occurs in a normal strain a sport results.

Potency is variable. Even in a pure strain a determiner does not always develop fully, and this is an important cause of individual variability. But in a heterozygote potency is usually more or less reduced. When the reduction is slight dominance is nearly complete; but when the reduction is great dominance is more or less incomplete and, in the extreme case, may be absent altogether. The series of cases of varying perfection of dominance described in this work illustrate at the same time varying potency. The extreme case is that of the rumpless fowl. The character in this case is an inhibitor of tail development. This character has arisen among vertebrates repeatedly and has become perpetuated in some amphibia and primates, including man. In the case of our cock No. 117, the action of the inhibitor is very weak, so that in the heterozygote the development of the tail is not interfered with at all and even in extracted dominants it interferes little with tail development, so that it makes itself felt only in reduced size of the uropygium and in bent or shortened back. But in No. 116 the inhibiting determiner is strong. It develops fully in about 47 per cent of the heterozygotes and 2 extracted dominants may produce a family in all of which the tail's development is inhibited. In the case of the rumpless condition that arose apparently de novo in my yards, the new inhibitor showed an intermediate potency completely stopping the tail development in 1 out of 25 heterozygotes. These three cases afford a striking illustration of a variation in the potency of the same inhibiting character in different strains.

Not only is potency variable, but its variations seem, in some cases, to be inheritable. This we have seen to be the case with the Y-comb ([p. 15]); with the extra-toed condition of Houdans ([p. 23]); and with rumplessness (cf. offspring of No. 117 as compared with No. 116, [p. 40]). On the other hand, the extra-toed condition of Silkies, the grade of clean shank, and the degree of closure of nostril seem not to be inherited.

D. REVERSION AND THE FACTOR HYPOTHESIS.

The brilliant development of the factor hypothesis, only dimly fore-shadowed by Mendel[17] (1866, p. 38), clearly expressed by Correns (1892), applied to animals by Cuénot, and further elaborated by Bateson and Castle and their pupils, has quite changed the methods of work in heredity. More forcibly than ever is it brought home to us that the constitution of the germ-plasm—not merely the somatic character—is the object of our investigation. With this principle fully grasped the existence of cryptomeres and the resolution of characters have become clearer. But the most striking result accomplished has been that of clearing up the whole range of phenomena formerly placed in the category of "reversion." No idea without a semblance of inductive explanation has been more generally accepted in the Darwinian sense both by professed biologists and practical breeders than this. Not only was the fact of recurrence of ancestral types in domesticated organisms accepted, but the idea that, in some way, hybridization per se destroyed the results of breeding under domestication was maintained.[18] Now we know that, under domestication, many races have been preserved that are characterized by a deficiency of a character or by a new, additional one, and that hybridization, by bringing together again those characters that are found in the ancestral species, may bring about again individuals of the ancestral type. There is nothing more mysterious about reversion, from the modern standpoint, than about forming a word from the proper combination of letters.

E. THE LIMITS OF SELECTION.

In the last few decades the view has been widespread that characters can be built up from perhaps nothing at all by selecting in each generation the merely quantitative variation that goes farthest in the desired direction. I have made two tests of this view, using the plumage color of poultry.

(1) Increasing the red in the Dark Brahma × Minorca cross.—The Dark Brahma[19] belongs to the group of poultry that contains a majority of characters derived from the Aseel type. Nevertheless, its plumage is closely related to that of the Jungle-fowl, from which it may be derived on the assumption that the red part of the pattern has become, for the most part, white. However, a little red remains on the middle of the upper feathers of the wing-bar. I crossed such a bird with a Black Minorca, and, as reported in my earlier work,[20] the offspring were all black, except that the males showed some red on the wing-bar. The amount of red varied in the different males, and I decided to test the possibility of much increasing the amount of the red by selection in successive generations. So I chose the reddest cock to head the pen. In this pen (No. 632) 222 chicks were produced and grew to a stage in which their adult color could be determined. Of these 222 chicks, 160, or 72 per cent, were black, without red; 24, or 10.8 per cent, were black with some red; 38, or 11.7 per cent, were typical Dark Brahmas, and 9 others, or 4.5 per cent, were modified Dark Brahmas.

The following year (pen 732) I bred a cock derived from the last year's pen, a bird that resembled much the male Dark Brahma (except that it was somewhat darker), to sundry hens, hybrids between the Dark Brahma and Minorca—some of the first and some of a later hybrid generation, but all black except that some of the 1906 birds had a little buff on the breast and the primaries. The F₁ (black) × F₂ (Dark Brahma) gave 51 per cent black offspring, 27 per cent with a black-and-red Game pattern, and 22 per cent with the Dark Brahma pattern devoid of red. Thus the third generation suddenly gave me a red-and-black Game-colored bird ([plate 12])!

My interpretation of the foregoing results is as follows: The Dark Brahma gametic formula proves to be CIrnwx, whereas the Black Minorca is C(IR)Nwx, where (IR) is equivalent to, and merely a further analysis of, the J of the formula of the Minorca as given in earlier sections. The I stands for the Jungle pattern without red and R is the red element in that pattern. Obviously N and R are the differential factors, 4 kinds of gametes occur in F₁, and in every 16 offspring these factors are combined in the following proportions: 9 NR, 3 Nr, 3 nR, 1 nr (compare the distribution of color types in the 222 offspring of pen 632). The F₂ male selected as father of the next generation (in pen 732) was an extracted Dark Brahma in coloration and probably formed only 1 kind of gamete, nr; but the hens were heterozygous in respect to N and R. Consequently 4 kinds of zygotes are to be expected in F₃; and expectation was realized as indicated in table 68.

Table 68.

	NnRr.	Nnr2.	n2Rr.	n2r2.
	Black with traces of red in male.	Black.	Game.	Brahma (without red).
	P. ct.		P. ct.	P. ct.
Expectation.	50		25	25
Realization.	51		27	22

In the case where both parents are F₂ or F₃ it is impossible to summate results, since the gametic formulæ of the different parents are so diverse; but the same types of solid blacks, black with trace of red in the males, Game-colored males and females, and Game with red replaced by white repeatedly occur. My plan of increasing red in the Dark Brahmas met with wholly unexpectedly prompt success, but not in the way anticipated. The result was not due to selection, but to the recombination of the factors necessary to make the Game plumage coloration.

(2) Production of a buff race by selection.—The second test was directed toward the production de novo of a new buff race from a Game fowl.

As is well known, all of our red and "buff" races, like the Buff Leghorn, Rhode Island Red, and others, have been derived from the Buff Cochin that came to us from China. The fact that a buff bird has, so far as I have been able to learn, not been produced in western countries indicates the probability that it can not be so produced at will; but the attempt seemed worth while.

I began with a Black Breasted Red Game because its plumage color is that of the primitive ancestor of domesticated poultry, and on that hypothesis the ancestor of the buff races. If these buff races were produced by extending the red through selection of the reddest offspring, that should be possible now as in the past.

A start in the direction of creating a buff bird would seem to require the elimination of the black. By crossing a black and red Game with a White Leghorn I got, in 1905, 2 white pullets with red on breast and some black specks. By crossing a Game Bantam (wingless) with a White Leghorn I got white birds with red present on wing-bar of male and breast of females and also some black spots.

In 1906 I mated 2 of these white (+ red) bantam hybrid hens with a hybrid cock and obtained again red on the wing-coverts of some white hybrids, while some were without red. From one of the hens I got 4 offspring, or 20 per cent of all, with buff on hackle-lacing, breast, and wing-coverts.

In 1907 I mated a prevailingly white male of the preceding year, that had red wing-bar, hackle, and breast, with the reddest females and obtained, along with pure whites and blacks and barred birds, these colors combined with red in various degrees, but not clearly in advance of the reddest of 1906. In 1908 I mated a white male, having red as in the Game, with my reddest hybrids. Again, white and white-and-buff birds appeared, but they showed no advance, except in one instance, among 138 young. This individual (No. 7950), derived exclusively from the Black-red Game and White Leghorn on one side and on the other from the White Leghorn-Game Bantam cross, had a uniform buff down. Unfortunately the chick quickly died.

The conclusion is that after three years of selection of the reddest offspring no appreciable increase of the red was observed—except for the remarkable case of one undeveloped chick with completely buff down. This, indeed, looks like a sport, or, perhaps, it is due to unsuspected factors. The experiment will be continued.

F. NON-INHERITABLE CHARACTERS.

So well-nigh universal is heredity that it is justifiable to entertain a doubt whether any character may fail of inheritance. So far as my experience goes, non-inheritable characters are such as are weak in ontogeny, so that they may readily fail of development even when conditions are propitious; or else they are so complex—so far removed from simple unit-characters—that their heritability in accordance with established canons is obscured. The first case is apparently illustrated by the rumpless cock (No. 117) and the wingless fowl; the second case by lop-comb and by right-and-left alternatives in general.

Apart from the distinct characters that fall under these two categories there are the fluctuating quantitative conditions. These depend for the most part, as already pointed out, on variations in the point at which the ontogeny of a character is stopped; and the stopping-point is, in turn, often, if not usually, determined by external conditions which favor or restrict the ontogeny. Whether or not such quantitative variations are transmitted is still doubtful. Our experiment in increasing qualities, such as redness in plumage-color, by selection of quantitative fluctuations have not been successful in the sense anticipated; neither have selections of comb, polydactylism, or syndactylism. Recently, prolonged attempts at the Maine Agricultural Experiment Station to increase egg-yield of poultry by selection have been without result. Apparently, within limits, these quantitative variations have so exclusively an ontogenetic signification that they are not reproduced so long, at least, as environmental conditions are not allowed to vary widely.

The conclusions which others have reached, and upon which de Vries has laid the greatest stress, that quantitative and qualitative characters differ fundamentally in their heritability is supported by our experiments.

G. THE RÔLE OF HYBRIDIZATION IN EVOLUTION.

The criticism has often been made of modern studies in hybridization that they are really unimportant for evolution because hybridization is uncommon in nature. Even at the beginning of the new era it could be replied that, first, we did not know how common hybridization might turn out to be in nature, and, second, that certainly in human marriage and among domesticated animals and plants, intermixing of characters played a most important part, and, finally, the laws of inheritance of characters were of such grave physiological import as to deserve study wholly apart from any question of the rôle of hybridization in evolution.

The last decade of work has made clear many things that were before uncertain. We now realize that in nature hybridization may and actually does proceed extensively. Dr. Ezra Brainerd has shown how many wild "species" of Viola have arisen by hybridization, as may be proved by extracting from them combinations of characters that are found in the species that are undoubtedly ancestral to them. In such highly variable animals as Helix nemoralis and Helix hortensis it is very probable that individuals with dissimilar characters regularly mate in nature and transmit diverse combinations of characters to their progeny. Indeed, if one examines a table of species of a genus or of varieties of a species one is struck by the paucity of distinctive characters. The way in which species, as found in nature, are made up of different combinations of the same characters is illustrated by the following example, taken almost at random. Among the earwigs is the genus Opisthocosmia, of which the 5 species known from Sumatra alone may be considered. They differ, among other qualities, chiefly in the following characters (Bormans and Kraus, 1900):

• Size: A, large; a, small.
• Wing-scale: B, brown; b, yellow.
• Antennal joints: C, unlike in color; c, uniform.
• Forceps at base: D, separated; d, not separated.
• Edge of forceps: E, toothed; e, not toothed.
• Fourth and fifth abdominal segments: F, granular; f, not granular.

The combinations of these characters that are found are as follows:

• Opisthocosmia ornata: AbcDEF.
• insignis: ABcDEf.
• longipes:AbCDEf.
• tenella: AbCdef.
• minuscula:aBCDEf.

Other species occur, in other countries, showing a different combination of characters, and there are characters not contained in this list, which is purposely reduced to a simple form; but the same principles apply generally.

The bearing upon evolution of the fact that species are varying combinations of relatively few characters is most important. Combined with the fact of hybridization it indicates that the main problem of evolution is that of the origin of specific characteristics. A character, once arisen in an individual, may become a part of any species with which that individual can hybridize. Given the successive origin of the characters A, B, C, D, E, F, in various individuals capable of intergenerating with the mass of the species, it is clear that such characters would in time become similarly combined on many individuals; and the similar individuals, taken together, would constitute a new species. The adjustment of the species would be perfected by the elimination of such combinations as were disadvantageous.

Cold Spring Harbor, New York,
May 20, 1909.