SEXUAL HORMONES AND MORPHOGENESIS 445 



is the same as in insects, every cell containing from the 

 beginning the catalyzers regulating the production of the sex 

 hormones in such quantities as are necessary for sexual differ- 

 entiation. He considers even the cock-feathering of old hens 

 as representing a state of intersexuality caused by the female 

 hormones being unable further to inhibit the action of the 

 male ones. There is no real basis for such an assumption, 

 which is founded only on analogy with insects. 



For mammals Lillies objections (1923) are very weighty. 

 " The opportunity for fusion of embryonic membranes from 

 a two-sided twin pregnancy is present from the lo-mm. stage 

 of the embryos, and as to vascular anastomosis from the 

 19-mm. stage, or slightly earlier. . . . This antedates the 

 beginning of visible sex differentiation ..." (Lillie, 1923, 

 pp. 61-62). So exchange of blood between twin embryos must 

 be possible before the beginning of sex differentiation. Now 

 Lillie examined a case of a freemartin in which fusion of the 

 membranes, according to his reconstruction of the probable 

 history of this case, was possibly complete at least at the 

 lo-mm. stage and a vascular anastomosis must have been 

 established at the same time. Such a case, according to Lillie, 

 would seem to have afforded the maximum opportunity of 

 masculinization by the hormones of the male partner on 

 account of the early time of onset and the long duration of 

 possible action. But, nevertheless, the modification of the 

 freemartin in this case was not particularly extreme. "It is 

 obvious," as Lillie says, "that the male sex hormone is acting 

 against resistance in the female soma ; moreover, this resistance 

 is not that of already differentiated parts, for the hormone is 

 introduced before sex differentiation ; it is rather a constitutional 

 resistance native to the determined sex. The phenomena can 

 be understood only on the assumption that the zygotic 

 sex-determining factors are also sex-differentiating factors in 

 mammals as in insects" (Lillie, 1923, pp. 71-72). "If there 

 were no other factors at work in determining the sex differentia- 

 tion of embryonic primordia than the specific sex hormone, it 

 is difficult to understand why the freemartin, which receives 

 only male sex hormones, should not become completely male" 

 (p. 71). .Besides this, interstitial cells to which the production 

 of male sex hormones is ascribed are found only from the 3-cm. 

 stage of the embryo onwards (Lillie and Bascom, 1922), i.e., 



