THE ENDOCRINAL ORGANS 449 



present. The individual without seminiferous tubules must, indeed, 

 be sterile, but he has the secondary traits of the male. This condition 

 occurs when the testes fail to descend into the scrotal sac. 



Although, according to present genetical opinion, primary sex differ- 

 ences are already determined in the fertilized egg by the chromosome 

 complex, there is, nevertheless, plenty of evidence that endocrines influ- 

 ence the secondary sex traits, the first striking evidence appearing at 

 puberty when the boy assumes some of his adult male characteristics. 

 That the chromatin constitution of the body cells has little or no influence 

 on sex is proved by the fact that, if ovaries are grafted in place of testes, 

 the individual takes on female characteristics. Crew cites the case of a 

 fowl which was successively a mother and a father as a result of the 

 destruction of the ovary by disease and subsequent growth of a testis in 

 place of the ovary. Further evidence of the influence of endocrines early 

 in development is afforded by the "freemartin." When a cow gives 

 birth to twin calves, one male and one female, the latter is sterile and 

 shows some male characteristics. In this case, the primary sex is prob- 

 ably determined in the fertilized eggs. But since the twin calves are 

 attached to a single placenta and share a common blood stream, the 

 male endocrine not only sterilizes the female, but also gives her masculine 

 traits from which she never recovers. Precisely how the male endocrine 

 dominates over the female is as yet an unsolved problem. 



THE FEMALE SEX GLANDS 



In the ovary, as in the testis, interstitial and germ cells may be dis- 

 tinguished. That the interstitial cells have an endocrinal function, is 

 suggested by the fact that they increase during pregnancy. The argu- 

 ment from analogy with the testis has less weight. 



There is also the following evidence that the Graafian follicles have an 

 endocrinal as well as a reproductive function. Before puberty, the 

 follicles mature in the ovary, but are not discharged. Instead, they 

 atrophy and the follicular liquid is reabsorbed into the blood, so that any 

 endocrine which the liquid may possibly contain enters the blood stream 

 to influence growth and development. 



At puberty, however, when a follicle, instead of degenerating, dis- 

 charges its egg, the follicular liquid stimulates changes in the uterus, 

 which prepare it for the implantation of the fertilized egg. At the same 

 time, correlated changes take place in the ovary. Of the follicular cells 

 which are left behind in the ovary when the ovum is discharged, some 

 undergo rapid multiplication and become converted into the fatty cells 

 of a corpus lutemn. (Fig. 344) 



The fate of the corpus luteum depends upon that of the ovum dis- 

 charged. If the ovum is fertilized and pregnancy occurs, the corpus 



