28 THE TESTIS AND ITS RELATION TO REPRODUCTION 



accessory organs reach a profound condition of regression in April and May. 

 Growtii of the new antlers starts at this time, and during the late summer the 

 antlers grow rapidly and begin to calcify. During the summer, also, the testes 

 develop rapidly, and spermatogenesis results. Loss of the "velvet" covering of 

 the antlers is experienced during September, and mating is the rule in October 

 and November. The antlers are shed in midwinter. If the testes are removed 

 after the naked antler condition is reached, the antlers are shed rapidly. Testos- 

 terone administered to does or to young males which have been castrated 

 induces the development of antlers. The general scheme of antler development 

 suggests, possibly, that the testicular hormone acts upon an anterior pituitary 

 factor, and this activated factor in turn initiates antler growth. Hardening of 

 the antlers and loss of velvet results from testosterone stimulation. Loss of 

 the antler is synchronized with a decrease in the amount of testosterone in 

 the blood stream, accompanied by the acquisition of a docile, non-belligerent, 

 more timid behavior. 



c) Effects upon the Seminiferous Tubules. Testosterone has a stim- 

 ulating effect upon the seminiferous tubule and sperm formation. This matter 

 is discussed in Chap. 3. 



d. Seminiferous-tubule Activity and Formation of Sperm 

 See Chap. 3. 



e. The Seminiferous Tubule as a Sperm-storing Structure 

 See p. 31. 



3. Role of the Reproductive Duct in Sperm Formation 



a. Vertebrates Without a Highly Tortuous Epididymal Portion of the 



Reproductive Duct 



In a large number of vertebrates, morphologically developed sperm pass 

 from the testis through the efferent ductules of the epididymis (vasa efferentia) 

 to the epididymal duct where they remain for varying periods. However, in 

 many vertebrates the anterior (proximal) portion of the sperm duct does not 

 form a tortuous epididymal structure similar to that found in other verte- 

 brates. This condition is present in the common frog, Rana; in the hellbender, 

 Cryptobranchus; in the bowfin, Amia; etc. Because of this fact, the sperm 

 pass directly into the vas deferens or sperm duct (Wolffian duct) without 

 undergoing a sojourn through a convoluted epididymal portion of the duct. 



Correlated with the type of testis and sperm-duct relationship in the frog, 

 is the fact that one may obtain viable, fertilizing sperm directly from the 

 testis. For example, if one removes the testis from a living frog and macerates 

 it in pond water or in an appropriate saline solution, active sperm are obtained 

 which are capable of fertilizing eggs in a normal manner. That is, the frog 

 testis matures sperm morphologically and physiologically. This type of tes- 



