164 THE PHYSIOLOGY OF REPRODUCTION 



In some animals the renewal of activity in the teates is associated 

 with the descent of these organs from their position in the abdominal 

 cavity through the inguinal canal and into a cutaneous fold. 1 This 



FIG. 50. Diagram illustrating the cycle of phases in spermatogenesis. 

 (From Schafer.) 



, Spermatogonia (seen dividing at 6) ; a', a", Sertoli cells ; 6, spermatocytes 

 (seen dividing at 5) ; c, spermatids ; s', parts of spermatids which dis- 

 appear when spermatozoa are fully formed ; s, seminal granules. 



1 Berry Hart, " The Nature and Cause of the Physiological Descent of the 

 Testes," Jour, of Anat. and Phys., vol. xliv., 1910. The author sums up the 

 essence of the process as follows : " The testis is united to a mammary area, 

 at first by the testicular caudal ligament and the inguinal fold or gubernaculum. 

 The developing gubernaculum, with the aid of the cremaster and peritoneum, 

 forms a pit or fossa for the testis in the Rodentia ; a more complete canal or 

 more or less pendulous scrotum in higher mammals. By subsequent dis- 

 proportionate growth of canal and testes, and finally (according to Frank) by 

 the involution and shrinkage of the gubernaculum, the testes in man become 

 permanently lodged in the scrotum." Numerous references to literature are 

 appended to this paper. When, as sometimes happens in man, one or both 

 of the testes do not descend or only imperfectly descend, the condition is said 

 to be one of cryptorchism. In cryptorchids spermatogenesis usually only takes 

 place for a short time after puberty (one or two years), if at all, and then the 

 seminiferous tissue degenerates, but the interstitial cells remain. Crew has 

 suggested that the aspermatic state of such testicles is due to the greater 

 temperature within the body as compared with the scrotum, and that the final 

 stages of spermatogenesis are inhibited by the higher temperature ("A 

 Suggestion as to the Aspermatic Condition, etc." Jour, of Anat., vol. Ixvi., 1922). 

 Guyer has made another suggestion, based on his work with spermatotoxic sera 



