THE PINEAL GLAND AND THE GONADS 777 



granules, staining black with osmic acid, are also present in the cyto- 

 plasm. The degree of development of the interstitial cells varies in dif- 

 ferent animals, being marked in the cat and man and ill-marked in the 

 rat and rabbit. In animals which show seasonal changes in sexual activ- 

 ity, the cells are most prominent between the periods of sexual activity, 

 when the semeniferous epithelium is less evident. They also become 

 prominent in cases where the semeniferous epithelium is atrophied, 

 either as a result of disease or following ligation of the vas deferens done 

 in such a way that the artery and nerves to the testicles are not included 

 in the ligature. When the testicle or a portion of it is grafted into 

 another part of the body, the semeniferous epithelium degenerates, but 

 the interstitial cells remain alive and become quite prominent. It is 

 believed that the interstitial cells are responsible for the production of 

 an autacoid that has to do. with the development of accessory sexual 

 characteristics. 



Tlie effects of castration are not significant in animals below the verte- 

 brata. In all of these, however, they are very pronounced. The cas- 

 trated male frog fails to show development of the thumb pad, but this 

 development immediately ensues if portions of testis from another frog 

 be placed in the dorsal lymph sac. In birds the results are more pro- 

 nounced; in the castrated male chick the comb, spurs, wattles, etc., fail to 

 develop, but will usually do so if some testis from another bird is trans- 

 planted into its tissues. In mammals the effects are most striking in 

 animals that develop marked male characteristics, such as the growth 

 of antlers in stags. These fail to develop properly and are prematurely 

 shed after castration. In man also, as is well-known from a study of 

 eunuchs, castration has a very profound effect. Hair fails to grow on the 

 face; the larynx remains undeveloped; the epiphyses are a long time in 

 ossifying, so that the stature may become great, but at the same time 

 the limb bones may be more delicate than usual ; the sutures of the skull 

 are slow in closing ; and the whole architecture of a castrated male comes 

 to be very like that of the female. Confirmatory evidence of the influ- 

 ence of the testicles on the development of secondary sexual character- 

 istics is afforded by the observation that malignant tumors of the testes 

 in boys are associated with the premature development of the secondary 

 sexual characteristics, and that these may recede after the removal of 

 the tumor. 



As a result of castration, interesting changes have also been observed 

 in other ductless glands. Thus, the suprarenal cortex and the thymus 

 become enlarged, whereas the thyroid and pituitary become atrophied. 

 The metabolic functions also become tardy, as is evidenced by a tendency 

 to the deposition of fat. 



