REGULATORS 607 



growths of one testis, and removal of the tumour has been 

 followed by their disappearance. 



A similar condition is associated with hypertrophic changes 

 in the cortex suprarenalis (p. 610), and with irritative changes in 

 the pituitary (p. 600). Whether these act through the testes 

 or directly is not known. 



(3) Transplantation — The first demonstration of the action 

 the endocrinetes was afforded by Berthold, who showed that 

 transplanting the testis into a capon leads to the develop- 

 ment of the typical sexual characters of the cock. This has 

 been fully confirmed by other observers in different species of 

 animals. 



(4) Extracts- — There is some evidence that in frogs the 

 development of sexual character may be produced by the adminis- 

 tration of testicular substance, but it is not quite satisfactory. 



The testis thus exercises an important influence on the 

 growth and development of the animal, and it does this by 

 yielding an internal secretion. That the source of this is the 

 interstitial cells is shown by the fact that ligature of the vas 

 deferens causes atrophy of the spermatogonia, and also in 

 course of time, of the cells of Sertoli, leaving only the inter- 

 stitial cells, and yet there is no arrest of the development 

 of the sexual characters. In the mole, these interstitial cells 

 reach their greatest development before the beginning of the 

 breeding season. 



In man they are well developed at birth, but disappear in 

 the course of the early weeks of life to reappear again at 

 puberty and to persist throughout life. 



B. Ovaries. 



(1) Removal of the ovaries has the same effect on the female 

 as removal of the testes has on the male. The development 

 of the secondar}' sexual organs, the uterus, mammee, etc., is 

 arrested. But, after removal of the ovaries, there is frequently 

 a tendency to develop the characters of the male. Thus, hinds 

 with diseased ovaries may develop horns and hen pheasants 

 and ducks may develop male plumage. The ovaries thus seem 

 to check the development of male characters. 



(2) Transplantation acts in the same way in the female as in 

 the male in preventing the effects of removal. In most animals 



