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
17272457983110........................54
272724591083110......1.........1373
37272494983110........................14
47273105983110...1...121...573
57273106983110........................21
68032457875229...11......247103
780324591075229..................1642
880331059752291.........422737
Totals (119)1221658283927
Percentages.5.35.34.47.124.834.523.9

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
9727121P.Dk. Brahma.1831P.Houdan10911662311......
10735142P.Mediterran.130P.Polish841........................
11735177P.Do.130P.Do.8...421..................
12735198P.Do.130P.Do.8...31......1............
Totals (56)1319972411......
Percentages23.234.016.112.53.67.11.81.8......
[A]12a813912F2Houd × Legh.23904F2Houd × Legh.7310311...............

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).