l.'4'2 MH. J. T. CUNNINGHAM ON 



'L'nns, including tlie sill^y eluvrivetei" of tlie featliers, contrasted 

 with the normal, we have seven pairs of characters the heredity- 

 of which is to be investigated. 



In the F, specimens the following characters are dominant : — ■ 



Coloured plumage. 



N(n'ma-1 structure of plumnge. 



Hose comb. 



Blac^k pigmentation of skin. 



IJouble hallux. 



Feathering of legs. 



Crest on heatl. 



But the dominance is somewliat irregular. Thus, one hen of 

 F| at the Gai'dens had a single comb. Seveival of the b\"s had a 

 normal foot on one side and a double hallux on the other. The 

 majority had the double hallux on both sides. In my pair the 

 cock has both feet normal and the hen has both feet abnormal, 

 with double hallux. This irregularity of dominance of the extra 

 toe has been noticed by previous expei-imenters. The crest is 

 dominant, but much smaller in the F/s than in the Silky. The 

 skin in my pair is pigmented, but not so dark as in the Silky ; it 

 looks blue instead of black. The feathered leg is dominant, the 

 feathering being present in all the F/s but the feathering is less 

 than in the Silky. These facts on the wliole agree with the idea 

 of dominance as the presence of a positive character (pi-esence 

 and absence theory of dominant and I'ecessive), which in the F^ 

 is present only in one half of the zygote, i. e., in one of the gametes 

 which are united in the cross, and therefore naturally does not 

 produce so much effect as when it is carried by botli gametes. 

 Thus the ci-est, the feathering of the legs, and the pigmentation 

 of the skin may be said to be intermediate in F, between the 

 conditions in the two parents. The dominance, however, seems 

 sometimes to fail, as in the case of the specimen with a single 

 comb, and the specimens with double hallux on one foot only or 

 on neither. The failure of dominance of the rose comb is not 

 mentioned by Bateson, who states that the dominance of the i-ose 

 comb is very definite and that it is generally quite impossible to 

 distinguish pure I'ose from the heterozygous type containing 

 single. On the other hand, exceptions to the dominance of the 

 extra toe are common, and are mentioned by Bateson, who states 

 that it occurs in all cases yet studied in birds and mammals. 



In all Fj specimens the coloured plumage and the normal 

 structure of the feathers are present ; these characters are 

 completely dominant. 



In other crosses which have been described in the experiments 

 above referred to much greater irregularity of dominance has 

 been observed. Thus Bateson found, with regard to the pig- 

 mentation of the skin, that when the Silky hen was crossed with 

 a Brown Leghorn cock all the Fj off*spring, both male and female, 



