SEX 87 



female organs leads to the appearance of male plumage. 

 The female, in such cases, carries the determiner for 

 male plumage, but its influence is prevented by an 

 inhibitor which goes with femaleness. Professor Mor- 

 gan has very recently made a remarkable experiment 

 which shows that this inhibitor is not a necessary conse- 

 quence of femaleness, but is associated with it. In the 

 breed of fowls known as the Seabright bantam, the 

 male bird is colored and has the feathers formed nearly 

 as in the female, instead of showing the typical plumage 

 of a cock. It occurred to Morgan that perhaps the in- 

 hibitor of typical male plumage had been developed in 

 the sexual organs of the male as well as those of the 

 female. He accordingly removed those organs from a 

 male, which then developed feathers like those of cock 

 birds of ordinary breeds ! 



9. The secretions or hormones which control the mani- Sexual 

 festation of sexual characters may so far influence sex of 



in 



as to produce sterility. It has been known from an- cattle and 



. . sheep 



cient times, that when cattle produce twins of opposite 

 sexes, the female is usually barren. Dr. Frank R. 

 Lillie of Chicago recently investigated this matter, and 

 found that the facts were as follows : The twins, repre- 

 senting different zygotes, have at first their separate 

 envelopes or chorions. As development proceeds, the 

 chorions fuse, and the blood .vessels of the two embryos 

 unite to form a single system. It results from this that 

 whatever secretions are produced by the one flow in the 

 veins of the other. The hormones from the male, 

 flowing through the body of the female, cause the sup- 

 pression of the reproductive organs of the latter. Oc- 

 casionally the envelopes of the two embryos remain 

 unfused, and in such cases, as Dr. Lillie was able to 

 demonstrate, the female is perfectly fertile. In sheep, 



