166 GENETICS AND EUGENICS 



barred Plymouth Rock fowls. In reciprocal crosses between 

 pure-bred barred Plymouth Rocks and black Langshans 

 (or any other unbarred breed), the results are not identical. If 



the barred parent is the male (Fig. 120 and Table 23), all Fi, 

 offspring are barred and in F2 all males are barred, but half the 

 females are black and half are barred. If, however, the barred 

 parent is the female (Fig. 121 and Table 23), all Fi males are 

 barred, but all Fi females are black. In F2 barred birds and 

 black birds occur in both sexes. These curious facts, which 

 have been repeatedly verified, suggest the occurrence of a 

 vehicle of inheritance which is duplex in males but simplex in 

 females. What this is we do not know. No chromosome has 

 been found which has a distribution of this sort in fowls, but 

 it is possible that some chromosome component, or other cell 

 constituent, has such a distribution and may be the actual 

 vehicle of inheritance in such cases. The most important 

 character economically, which appears to be affected by some 

 sex-linked factor in poultry, is fecundity. Pearl has observed 

 that when reciprocal crosses are made between Cornish In- 

 dian games, a poor breed for winter egg production, and 

 barred Plymouth Rocks, a fairly good breed for winter egg 

 production, the Fi females in each case resemble the father's 

 race more strongly than the mother's race as regards egg 

 production. Pearl did not maintain, however, nor do his ex- 

 periments suggest, that the inheritance of fecundity depends 

 exclusively upon a sex-linked factor. Goodale, however, has 

 not been able to confirm Pearl's observations, in the case of 

 Rhode Island Red fowls. He finds no evidence of superior 

 influence of the sire in the transmission of racial fecundity. 



