26 



THE TESTIS AND ITS RELATION TO REPRODUCTION 





Fig. 14. Sections of the testis of the stickleback (Gasterosteus pungitius). (Modified 

 from Moore, '39, after Van Oordt.) Cf. fig. 13. (A) Spermatogenic activity with many 

 formed sperm in seminiferous tubules before the mating season, interstitial tissue in 

 abeyance. (B) At mating period. Interstitial tissue well developed, spermatozoa stored 

 in the tubules with spermatogenic activity absent. 



- ^:^\^^^^^f^^^^v^'^^^.^^k^^v^^^^^^^^j 

 APRIL MAY JUNE JULY AUG 



SEPT. OCT. 



Fig. 15. Seasonal reproductive cycle in the stickleback (Gasterosteus aculeatus). Cf. 

 fig. 14. Breeding season is indicated by crosshatching below base line. Observe that 

 spermatogenic activity follows rise of temperature, whereas interstitial-tissue and sex- 

 character development occur during ascending period of light. (Redrawn from Turner; 

 General Endocrinology, Philadelphia, Saunders, modified from Craig-Bennett, 1931.) 



c. Testicular Control of Body Structure and Function by the Male 



Sex Hormone 



1) Sources of the Male Sex Hormone. Testosterone is prepared from tes- 

 ticular extracts. It is the most potent of the androgens and is believed to be 

 the hormone produced by the testis. The chemical formula of testosterone is: 



OH 



CHa 



^\ 



