SEXUAL ORGANS 641 



seen that, so long as a portion of one testicle remains, the male 

 characters are preserved, but after removal of this residue the 

 comb and wattles wither in a few weeks (Hanau). At the breeding- 

 time the muscles of the forearm of the brown land frog (Rana 

 fused) become hypertrophied in the male, so that it can more tightly 

 hold the female. At the same time the balls of the toes increase 

 in size, and become covered with a peculiar black growth. After 

 the breeding season these secondary sexual characters disappear. 

 If the male frog is castrated, the periodic return of these phenomena 

 does not occur, but the presence of one testicle suffices for their 

 development on both sides. When pieces of testicle from normal 

 frogs are introduced under the skin of the castrated frogs, the 

 phenomena occur just as if the animals had not been castrated 

 (M. Nussbaum). 



Many facts indicate that the internal secretion is not furnished by the 

 proper reproductive elements (those which form the spermatozoa), 

 but by the interstitial cells of Leydig, which are distributed in groups 

 throughout the substance of the testes between the seminal tubules. 

 The spermatogenic cells may be atrophic or absent, as in cryptorchids, 

 or after ligation of the vas deferens (Bouin and Ancl) ; or they may be 

 destroyed^ by X-rays, without interfering with the development of the 

 secondary sexual characters. Steinach has shown that when the testes 

 of a young rat or guinea-pig are transplanted to another part of its 

 body (the peritoneal cavity or subcutaneous tissue), the animal de- 

 velops all the secondary sexual characters at the proper time. The 

 penis grows to the normal size. The seminal vesicles and prostate 

 develop in the ordinary way, and yield a plentiful secretion. Sexual 

 desire and potency appear in due season, and in normal or, in not a few 

 cases, indeed, increased intensity. Yet histological examination shows 

 that not a single spermatocyte or spermatid (Chapter XIX.) has de- 

 veloped, while outside the seminal tubules the interstitial cells form 

 large masses which much surpass in size the interstitial islands of the 

 normal testis. Similar changes are observed, though with less cer- 

 tainty and after a longer interval, when the vas deferens is ligated, a 

 method often recommended and occasionally practised for the steriliza- 

 tion of the human male. On account of the influence, thus demon- 

 strated, of the interstitial cells in producing the sexual development 

 observed at puberty, Steinach designates these cells collectively as the 

 'puberty gland.' 



When the ovaries of a young female rat or guinea-pig are trans- 

 planted into the peritoneal cavity or under the skin of a previously 

 castrated male animal of the same land (preferably, to facilitate accurate 

 comparison, a male of the same litter), only the interstitial cells 

 survive (in about half the cases). There is this difference in the fate, 

 of the ovary and the testis when auto-transplanted,* that the genera- 

 tive elements of the former, the Graafian follicles, with the ova contained 

 in them, generally develop as well as the large interstitial cells rich 

 in protoplasm lying in the stroma, which cells appear to constitute 



* An auto-transplant or auto-graft is a portion of tissue transplanted into 

 another part of the same animal's body. A homceo-graft is a portion of tissue 

 1 ransplanted i nto the body of another individual of the same species; a hetero- 

 graft is a portion of tissue transplanted into an animal of a different species. 



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