DEVELOPMENT OF REPRODUCTIVE SYSTEM 



801 



2 PROTOPTERUS 



J W K 



Q POLYPTERUS 5 AMIft 



N. 



J SiLMONID 



Fig. 351 — (Continued) 



See legend on pp. 798 and 799. 



35 IC). The blind caudal end of the invagination grows posteriorly along 

 the side of the mesonephric duct to join the cloaca (fig. 351C-2). 



a. Male Reproductive Duct 



The developing gonad of the males of Amphibia, reptiles, birds, and mam- 

 mals, together with the elasmobranch and ganoid fishes, appropriates the 

 mesonephric duct for genital purposes. In this appropriation, the rete tubules 

 of the testis unite with certain of the mesonephric tubules. The latter form 

 the vasa efFerentia or efferent ductules of the epididymis (fig. 351A-C). In 

 teleosts, dipnoan fishes, and Polypterus, the marginal testicular duct becomes 

 modified into a vas deferens which conveys the genital products to the uro- 

 genital sinus (fig. 351F-H). 



In all vertebrates and in some mammals (Chap. 1), the testis remains 

 within the abdominal cavity. However, in most mammals and in the flatfishes, 

 there is a posterior descent of the testis (figs. 3 and 5) into a compartment 

 posterior to the abdominal cavity proper. 



