ACTIVITIES OF THE MALE REPRODUCTIVE SYSTEM 



25 



(LH; ICSH), the seminiferous tubules of the testis respond and spermato- 

 genesis occurs. However, the interstitial tissue remains relatively unstimu- 

 lated and the accessory structures continue in the atrophic state. If larger 

 doses of the luteinizing factor are given, the interstitial tissue responds and 

 the secondary sexual characters are developed, showing a relationship between 

 interstitial activity and sex-hormone production. (Consult Evans and Simpson 

 in Pincus and Thimann, '50, pp. 355, 356.) 



From certain species whose reproductive activities are confined to a par- 

 ticular season of the year, there also comes evidence that the interstitial tissue 





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4) " 



%. i 



a?) e *■ • «4,^» , „, B 



Fig. 13. Sections of seminiferous tubules of silver fox. (After Bishop.) (A) Re- 

 gressed state of tubules following breeding season. (B) Tubule from fox during the 

 breeding season, characterized by active spermatogenesis. 



is the site of sex-hormone production. In the behavior of testicular tissue in 

 the stickleback, Gasterosteus, as shown by van Oordt ('23) and Craig-Bennett 

 ('31) sperm are produced actively in the seminiferous tubules during one 

 period of the year when the interstitial tissue is in an undeveloped condition. 

 The secondary sex characters also are in abeyance at this season of the year. 

 However, during the months immediately following sperm production, sperm 

 are stored within the seminiferous tubules and active spermatogenesis is absent. 

 When the seminiferous tubules thus have completed their spermatogenic ac- 

 tivity, the interstitial tissue begins to increase, followed by a development of 

 secondary sex characteristics (figs. 14, 15). A similar difference in the rhythm 

 of development of these two testicular tissues can be shown for many other 

 vertebrates. All of these suggestive facts thus serve to place the responsibility 

 for male sex-hormone production upon the interstitial tissue, probably the 

 cells of Leydig. 



