254 H. D. GOOD ALE 



pected occurrence of such characters as a broad neck ring in the 

 males and the appearance of a neck ring, plain head and black 

 individuals among the females, is probably due to the presence 

 of cryptomeres in the Pekins, though this point cannot be proved 

 until further crosses with other varieties of ducks are made. 

 Ridgeway, however, mentions in passing a cross between Mus- 

 covy (black) and Aylesbury (white). The progeny were colored 

 like mallards. His figure shows a very broad neck ring. 



Thus, in many respects Fi in the present instance, is like an F2 

 generation. The F2 generation in these experiments contains 

 only a few more forms than Fi. Indeed, with larger numbers, 

 some of the forms which have appeared only in F2 may reasonably 

 be expected to appear in Fi. A priori, it would seem more prob- 

 able that the heterozygous males occurred among the Pekins. 

 The Pekins may easily be a mixed population in respect to numer- 

 ous factors rendered invisible by the white plumage. Some 

 individuals may be heterozygous in respect to a given character 

 while others may be homozygous either for the presence of this 

 character or for its absence. The introduction of color has made 

 possible the isolation of pure lines. 



As the individual mothers of the Fi generation are unknown, it 

 is obvious that if one mother were homozygous for a character 

 and another heterozygous, the father being homozygous, that 

 the observed results would follow, provided that it is also assumed 

 that in the female a character does not become patent except in 

 the homozygous condition, though patent in its heterozygous 

 condition in the males. Thus the case would be paralleled to the 

 inheritance of horns in sheep, cited by Bateson. 



Not all characters appear to be correlated with sex. White 

 shading of the breast and red-white on the dorsal wing surface is 

 present in some Fi individuals of both sexes, absent in others, 

 thus behaving as if it were of the form DR in both parent stocks, 

 or DR in one and RR in the other. The evidence, however, is 

 conclusive that at least one of the parent stocks contains individ- 

 uals which are heterozygous for certain characters. 



