Experiments with Poultry 121 



rather than involving the selection of extreme somatic fluctua- 

 tions. These two kinds of selection may be superficially similar, 

 but involve in reality an important difference in principle. 



Experiments with Poultry 



The different breeds of poultry have furnished Bateson and his 

 co-workers with excellent material for experimental study. The 

 domesticated breeds differ not only in color, but also in the char- 

 acter of the combs, in the feathered or unfeathered condition of 

 the shanks, in the number of toes, in crested and uncrested heads, 

 and the habit to sit or not to sit on the eggs. These characters 

 are inherited discontinuously, showing dominance and recessive- 

 ness, and also often giving the Mendelian ratio. 



In his earlier work (begun in 1898 and published in 1902), 

 Bateson used principally Indian Game and white Leghorn, 

 but subsequently brown, and white Dorkings and one Wyan- 

 dotte were used. He found that as a rule pea comb, rose comb, 

 and extra toe are dominant characters, while single comb and 

 normal foot are recessive. Nevertheless, the first generation 

 sometimes shows blending in various degrees, and in consequence 

 the dominance may be considerably reduced. When the jPj's 

 are inbred, some of their offspring show one character, and 

 others the other "in proportions following Mendel's law with 

 some consistency," but here again the results do not always 

 conform to the expectation. Other conflicting results are also 

 recorded that are difficult to explain. 



In a recent communication (published in 1905) by Bateson and 

 Punnett further details are given ; and in a supplementary paper 

 by C. C. Hurst, some experiments with Leghorns, Houdans, 

 black Hamburgs, and buff Cochins are described. As the re- 

 sults of Hurst are more easily presented in a less technical form, 

 I have relied on them mainly in the following account. 



The leaf comb of the Houdan is dominant over the single comb 

 of the Leghorn and Cochin. In a few cases the dominance is 

 complete, but in the majority of cases it is incomplete interme- 

 diate combs being produced. 



