36 THE GENETIC AND THE OPERATIVE EVIDENCE 



tion of the germ-cell by X-rays has no effect on the secondary sexual 

 characters. 



This threefold evidence demonstrates that in the male of the mam- 

 malia most, perhaps all, of the secondary sexual characters that are 

 affected by castration are not affected by the destruction of the germ- 

 cells. This conclusion supports very strongly the view that the inter- 

 stitial cells are the cellular element in the testes that influence through 

 internal secretion the development of the secondary sexual characters 

 of the male. 



Equally important are the results that relate to the accessory organs 

 of reproduction, such as the glands that open into the vas deferens 

 (prostate, Cowper's gland, etc.) and the copulatory organs also. In 

 the castrated mammals these organs diminish in size. On the other 

 hand, after destruction of the germ-cells in the testes (or even when 

 they fail to develop as in cryptorchid individuals) these accessory parts 

 are unaffected. In birds, as will be shown, the situation is entirely 

 different. 



CYCLICAL CHANGES IN THE INTERSTITIAL CELLS IN 

 HIBERNATING MAMMALS. 



The changes that take place in the interstitial cells in mammals that 

 hibernate and in which there is a definite rutting season following 

 hibernation have been examined by several workers. The mole has 

 been studied by Regaud (1904), Lecaillon (1909), Tandler and Grosz 

 (1911); the marmot by Hauseman (1895) and Gaugini (1903); the 

 hedgehog by Marshall (1911); and the woodchuck by Rasmussan 

 (1917). In the mole the interstitial cells are most abundant when the 

 tubules in which the spermatogenesis is taking place are least devel- 

 oped, and vice versa. In the hedgehog the increase in both tissues takes 

 place at the same time. In the woodchuck both tissues increase rapidly 

 after hibernation (during March and April), after which the spermato- 

 genesis continues actively for the two following months (May and 

 June), while the interstitial cells retrograde rapidly during April and 

 remain at a low level for the rest of the year. Retrogression in the 

 germinal epithelium begins in July, after the rutting season is past. 

 It appears from this evidence that the activity of the two tissues does 

 not always run the same course. Since the secondary sexual characters 

 of the male, which are not well developed in these animals, are not so 

 far as known affected by the condition of the testes, the evidence does 

 not have any very direct bearing on our present topic. How far the 

 sexual behavior of these mammals is determined by the quantity or by 

 the activity of the interstitial cells is not very clear from the evidence, 

 although there is a very noticeable increase in the amount of this 

 tissue just before and during the rutting season. In the mole also the 



