TABLE OF CONTENTS.

PAGE
Introduction[3]
Chapter I. The Split or Y Comb[5]
A. Interpretation of the Y Comb[5]
B. Variability of the Y Comb and Inheritance of the Variations[12]
Chapter II. Polydactylism[17]
A. Types of Polydactylism[17]
B. Results of Hybridization[18]
Chapter III. Syndactylism[29]
A. Statement of Problem[29]
B. Results of Hybridization[32]
Chapter IV. Rumplessness[37]
Chapter V. Winglessness[42]
Chapter VI. Booting[43]
A. Types of Booting[43]
B. Normal Variability[43]
C. Results of Hybridization[46]
Chapter VII. Nostril-Form[59]
Chapter VIII. Crest[67]
Chapter IX. Comb-lop[69]
Chapter X. Plumage Color[71]
A. The Gametic Composition of the Various Races[71]
1. White[71]
2. Black[72]
3. Buff[72]
B. Evidence[72]
1. Silkie × Minorca (or Spanish)[72]
2. Silkie × White Leghorn[75]
3. Silkie × Buff Cochin[76]
4. White Leghorn × Black Minorca[77]
5. White Leghorn × Buff Cochin[77]
6. Black Cochin × Buff Cochin[78]
Chapter XI. Inheritance of Blue Color, Spangling, and Barring[79]
A. Blue Color[79]
B. Spangling[80]
C. Barring[81]
1. White Cochin × Tosa[81]
2. White Leghorn Bantam × Dark Brahma[82]
3. White Leghorn Bantam × Black Cochin[82]
Chapter XII. General Discussion[85]
A. Relation of Heredity and Ontogeny[85]
B. Dominance and Recessiveness[88]
C. Potency[92]
D. Reversion and the Factor Hypothesis[93]
E. The Limits of Selection[94]
1. Increasing the Red in the Dark Brahma × Minorca Cross[94]
2. Production of a Buff Race by Selection[95]
F. Non-inheritable Characters[96]
G. The Rôle of Hybridization in Evolution[97]
Literature Cited[99]

INHERITANCE OF CHARACTERISTICS
IN DOMESTIC FOWL.
BY
CHARLES B. DAVENPORT.

[2]

INTRODUCTION.

A series of studies is here presented bearing on the question of dominance and its varying potency. Of these studies, that on the Y comb presents a case where relative dominance varies from perfection to entire absence, and through all intermediate grades, the average condition being a 70 per cent dominance of the median element. When dominance is relatively weak or of only intermediate grade the second generation of hybrids contains extracted pure dominants in the expected proportions of 1:2:1; but as the potency of dominance increases in the parents the proportion of offspring with the dominant (single) comb increases from 25 per cent to 50 per cent. This leads to the conclusion that, on the one hand, dominance varies quantitatively and, on the other, that the degree of dominance is inheritable.