94 A MANUAL OF MENDELISM 



for the males can only take the free factor b from their 

 sires, but must take B from their dams, while the 

 females can only take the free factor b from their 

 sires but must take the tied factor b from their dams. 

 Dr. Pearl mated Cornish Indian Game cocks, which are 

 black and unbarred, with Barred Plymouth Rock hens, 

 and their adult progeny consisted of 95 males, all 

 barred, and 96 females, all unbarred. 



Professor Castle of Harvard, in his volume " Heredity 

 in Relation to Evolution and Animal Breeding," tells 

 of another test which is really similar to that of the 

 Barred Plymouth Rock fowl producing unbarred females, 

 with the addition that the numbers of each kind of 

 progeny are counted. He tells us that when hybrid 

 cocks are mated either with hybrid hens or with Barred 

 Plymouth Rock hens, which are hybrid for barring, the 

 progeny are again male and female in equal numbers, 

 but, while the cocks are all barred, half the hens are 

 barred, the other half unbarred. This is exactly accord- 

 ing to expectation, for 



MM ^ M 

 B b ^""^B 



should MM MM M 

 produce BB Bb B 



The cocks must take B from their dams, but they may 

 take either B or the untied b from their sires, while the 

 hens must take the tied b from their dams and either 

 B or b from their sires. 



Thus the double hypothesis that hens are hybrids and 

 that non-barring is coupled with femaleness is sound. 



But there are other factors coupled with that for 

 femaleness. In addition to the Plymouth Rocks, there 



