356 EVOLUTION, GENETICS, AND EUGENICS 



are inbred tend to liberate latent characters when the ordinary course 

 of breeding is departed from. 



Hurst contrasts the following characters, which usually show them- 

 selves dominants and recessives; but it has to be admitted that the 

 dominance — always complete for some characters — is for others fre- 

 quently, or even always incomplete — i.e., showing traces of the corre- 

 sponding recessives. 



Dominant Characters Recessive Characters 



Rose comb Leaf comb, single comb 



White plumage Black plumage, buff plumage 



Extra toes Normal toes 



Feathered shanks Bare shanks 



Crested head Uncrested head 



Brown eggs ^A^lite eggs 



Broodiness Non-broodiness 



Davenport's copiously illustrated work is also of great interest. 

 He shows in case after case that the character dominant in the first 

 hybrids is more or less influenced by the recessive character. Polish 

 fowls with a large hernia of the brain on the top of the head were 

 paired with Minorcas with normal heads. The hybrids showed no 

 hernia, but most of them showed a frontal prominence. When the 

 hybrids were inbred the hernia occurred in 23.5 per cent — a. close 

 approximation to the theoretical 25 per cent. 



Single-combed black Minorcas were crossed with white-crested 

 black Polish fowls with a very small bifid comb. The hybrids had 

 combs single in front, split behind. When the hybrids were inbred 

 there resulted in a total of 10 1 offspring, 29.7 per cent with single 

 combs (like Minorcas), 46.5 per cent with Y-shaped combs, and 23.8 

 per cent with no combs or only papillae (like the Polish forms). Here, 

 again, the result is in a general way Mendelian, but the Y-like comb 

 is a complication. 



Pigeons. — R. Staples-Browne crossed a web-footed pigeon (an 

 occasional discontinuous variation) with a normal form, and got six 

 normal young. In other words, the web-foot character is recessive 

 to the normal foot character. The hybrids were inbred, and in one 

 case produced nine with normal feet and three with webbed-feet — a 

 Mendelian splitting-up. But from another pair of hybrids seventeen 

 normal offspring resulted. Thus, the illustration of Mendelian 

 inheritance is inconclusive. Besides the numbers were too small. 



We have noticed elsewhere that crossing different breeds of pigeons 

 often results in forms which more or less resemble the reputed original 



