32 REPRODUCTIVE SYSTEM OF THE ADULT FROG 



The testes are whitish and ovoid bodies lying ventral to and near 

 the anterior end of each kidney. The vasa efferentia, ducts from the 

 testes, pass between the folds of the mesorchium and into the mesial 

 margin of the adjacent kidney. During the breeding season, or after 

 slight compression of the testis of the hibernating frog, these ducts be- 

 come the more apparent due to the presence in them of whitish masses 

 of spermatozoa in suspension. The ducts are very small in diameter, 

 tough walled, and interbranching. They are lined with closely packed 

 cuboidal cells. Each duct is connected directly with a number (8 to 

 12) of Malpighian corpuscles of the kidneys, by way of the Bow- 

 man's capsules. These connections are permanent so that many of 

 the anterior uriniferous tubules of the frog kidney will contain sperma- 

 tozoa during the breeding season. The presence of spermatozoa in 

 the kidney also can be achieved artificially by injecting the male 

 frog with the anterior pituitary sex-stimulating hormone. Since these 

 anterior Malpighian corpuscles carry both spermatozoa (during the 

 breeding season) and excretory fluids (at all times), they are truly 

 urogenital ducts having a dual function. This situation does not hold 

 for higher vertebrates. 



The spermatozoa are produced in subdivisions of the testes known 

 as seminiferous tubules. These are closely packed, oval-shaped sacs, 

 which are separated from each other by thin partitions (septula) of 

 supporting (connective) tissue known as interstitial tissue. This tissue 

 presumably has some endocrine function. The thickness of this 

 tissue is much reduced immediately after breeding or pituitary stimu- 

 lation. The interstitial tissue is continuous with the covering of the 

 testes known as the tunica albuginea, and the whole testis is enclosed 

 in the thin peritoneal epithelium. 



Spermatogenesis. 



Shortly after the normal breeding season in the spring for Rana 

 pipiens, the spermatogonium, which has ceased all mitotic activity, 

 enters upon a period of rest but not inactivity. During this period the 

 nucleus passes through a sequence of complex changes which repre- 

 sent an extended prophase. This is in anticipation of the two matura- 

 tion divisions that finally produce the haploid spermatid which 

 metamorphoses into a spermatozoon. 



The nucleus of the spermatogonium contains chromatin which ap- 

 pears as relatively coarse lumps distributed widely over an achro- 



