xi REPRODUCTIVE ORGANS AND THE FAT BODIES 215 



The males of several species of Rana possess a curious 

 homologue of the oviduct of the female. In Rana pipiens 

 it is very well developed, and contains an enlargement at its 

 posterior end representing a uterus. It lies just external to 

 the ureter, and extends as a fine tube some distance in front 

 of the kidney. Its function, if it has any, is unknown. Cases 

 are not uncommon in which organs characteristic of one sex 

 are found in a rudimentary form in the other, and it is not 

 improbable that the oviduct of the male frog is simply a use- 

 less, although rather large, rudiment of this kind. In the 

 bullfrog {Rana Catesbiana) this duct is absent. 



Organs of the Male. - The testes are rounded or ovoid 

 organs lying ventral to the kidneys. Like the ovaries, they 

 are surrounded by peritoneum, which is extended dorsally 

 as a double membrane, the mesorchium, to the dorsal side 

 of the body cavity, where it becomes continuous with the 

 general coelomic lining. The vasa efferentia, or ducts of 

 the testes, consist of a variable number of slender tubes, 

 which extend within the mesorchium to the inner margin 

 of the kidney, where they connect with Bidder's canal. The 

 vasa efferentia often branch and anastomose more or less, 

 in a way which varies greatly in different individuals. 



The testis is made up essentially of a mass of tubules, 

 together with blood vessels and nerves, and a small amount 

 of connective tissue binding the tubules together. The whole 

 is surrounded by a connective tissue membrane, the tunica 

 albuginea, outside of which is the peritoneum. Toward the 

 outer portion of the testis the tubules extend radially, and 

 end blindly next to the tunica albuginea. Near the point 

 where the vasa efferentia enter they become coiled irregu- 

 larly. The vasa efferentia form a network within the testis, 

 into which the tubules open at their inner ends. Each 

 tubule possesses an outer membrana propria and an inner 



