CH. LIX.] SECONDARY SEXUAL CHARACTERS 879 



Thus in the cock castration arrests the development of the comb and 

 spurs ; in the stag of the antlers. In the eland and in horned cattle 

 where both sexes have horns, their growth is not inhibited by 

 castration, though their shape may be affected (Marshall). In 

 Herdwick sheep, where the males are horned and the females horn- 

 less, it has been shown that the presence of the testes is essential, 

 not merely for the initiation but also for the continuance of horn 

 growth. Castration stops further horn growth forthwith, and at 

 every stage of development. 



Ligature of the vas deferens leads to atrophy of the seminiferous 

 tubules, whilst the interstitial cells are not affected, and the 

 secondary sexual characters develop as usual. It is on this ground 

 that most investigators agree that the interstitial cells of the testis 

 are the source of the internal secretion. These cells have all the 

 appearances of secreting cells, and their full development coincides 

 with the first appearance of spermatogenesis. Transplantation of a 

 testis in an abnormal position in the body cavity is followed by 

 development of the secondary sexual characters, and the view is 

 generally held that the internal secretion acts chemically on the 

 parts concerned, rather than through the intermediation of the 

 nervous system. 



The Prostate. As already stated, the removal of the testis leads to atrophy of 

 the prostate, but the converse has been stated to be also true, and that in dogs 

 prostatectomy causes the testes to lose their functional activity. Attempts to 

 repeat these effects, by other observers, have, however, failed, and as Marshall 

 points out, it is unlikely, on phylogenetic grounds, that the functions of the 

 essential reproductive organ should depend upon the presence of an accessory 

 gland of comparatively late appearance in the history of evolution. 



The Ovary. Extirpation of the ovaries prevents the onset of 

 puberty and the occurrence of menstruation, but produces no 

 noticeable effects on the general form and appearance of a woman. 

 Ovariotomy after puberty brings menstruation to an end, and there 

 may be slight atrophy of the breasts, uterus, and external genital 

 organs ; this, however, does not always occur. 



In animals the same operation prevents the occurrence of the 

 cestral cycle, but the " periods " continue to recur if one of the ovaries 

 is grafted into the abdomen. 



The ovary does not appear to have such far-reaching effects on 

 general metabolism as the testis possesses; its internal secretion 

 seems to act especially upon the uterus. Marshall's observations 

 on dogs, and Heape's on monkeys, favour the view that the 

 interstitial cells of the ovary are responsible for the production of a 

 hormone which initiates the cestrous cycle, and if this is the case the 

 occurrence of menstruation in the human female is attributable to 

 the action of the same cells. 



