GENERAL DISCUSSION. 65 



D. GENERAL DISCUSSION. 



INHERITANCE OF PARTICULAR CHARACTERISTICS. 



COMB FORM. 



The (comBjis a characteristic that has had its origin in the genus Callus. 

 It consists of a mass of uncovered erectile tissue a tissue present in many 

 species of birds. The primitive form of the comb is the single comb seen 

 in the wild species of the genus Gallus, and in most domestic races. This 

 may beimodifieiLiii-iwo directions : First, in the direction of lateral repetition 

 of the comb giving rise to the pea comb,* and, in an extreme case, to the 

 rose comb (of which the walnut comb of the Malays is a special modifica- 

 tion); second, in the direction of reduction of the modified comb producing 

 the races with mere papillae (Houdan, Polish, La Fleche, etc.) or that are 

 entirely combless (Breda fowl). That the rose comb is a modification of the 

 same sort as the pea comb but carried to a greater extreme is indicated by 

 the fact that the rose comb often shows five parallel ridges (instead of the 

 more usual irregularly scattered papillae) and that in the female the rose 

 comb sometimes consists of three ridges as in the male pea comb. 



When single comb (Minorca, fig. 4) and pea comb (Brahma, fig. 19) are 

 crossed, pea comb is dominant (p. 35). The median ridge is, however, in 

 the hybrid high for a pea comb and the lateral ridges are usually reduced 

 (figs. 20, 21 ). When single comb (Leghorn) and rose comb (Minorca) are 

 crossed, rose comb is dominant (p. 30). When single comb (Minorca or 

 Leghorn) is crossed with the paired rudiments of a comb found in the Polish 

 and Houdan fowl, a Y-shaped comb results (pages 10, 22, 28, fig. 8). This 

 Y comb is of great interest. It was obtained by Bateson and Punnett (1905, 

 pp. 108, 112-114) i n some of the offspring of (single- comb Leghorn x rose- 

 comb Dorking), crossed with (single-comb Leghorn x walnut- comb Indian) ; 

 and also in one of the offspring of a single-comb Leghorn crossed with 

 [(single-comb Leghorn x walnut-comb Indian) x (single-comb Leghorn 

 X rose- comb Dorking)]. In Bateson and Punnett' s cases the splitting was 

 evidently nearly complete, forming an 0-shaped comb, or the ' ' cup comb ' ' 

 of Darwin (1876, Chapter VII). The Y comb was obtained also by Hurst 

 (1905, pp. 133, 135, 138, 140, 146). This was a single split comb when 

 Leghorn and Houdan were crossed, and a rose split comb when rose-comb 

 Hamburgh and Houdan were mated. 



\] The interrelation of the different forms of comb single, pea, walnut, 

 Y, and V may, I think, be expressed in the following hypothesis : The pea 

 comb and the walnut comb are composed of two elements a median single 

 comb and a pair of lateral combs. This hypothesis is supported by the 



* The pea comb was doubtless a characteristic of the unknown feral ancestor of the 

 Aseel-Indian group. But as the single comb is the dominant type in the known wild 

 Jungle fowls the pea comb probably evolved from it. 

 5 



