240 THE MALE REPRODUCTIVE SYSTEM 



the anterior mesonephric tubules proliferate to extend as cords 

 into the region of the developing seminiferous tubules. Such meso- 

 nephric derivatives unite with the cords forming in the testis, both 

 develop lumens, and the numerous seminiferous tubules acquire an 

 outlet through the modified mesonephric tubules, now called vasa 

 efferentia, to the Wolffian duct. The whole anterior end of the 

 Wolffian duct may become much convoluted to form the epididymis, 

 a special part of the duct system, to be described later. In the 

 amniotes the entire Wolffian duct is no longer urinary, but becomes 

 the vas deferens, or main sperm duct, of the male. Variations 

 exist through the ascending groups as regards the completeness of 

 a separation of the two systems. In cyclostomes the sperm may 

 have no duct system, but pass directly to the coelome and out 

 through abdominal pores; in mammals the sperm pass through the 

 converted mesonephric duct system independent of the urinary 

 system until it joins the urethra, in the vicinity of the copulatory 

 organ, the penis. 



In general, the sperm ducts are lined with a cuboidal epitheliiun 

 where they unite with the seminiferous tubules, but approaching 

 the posterior portions the epithelium changes to columnar, and in 

 the vas deferens it may become stratified cohunnar. Ciliated cells 

 often alternate with those of glandular types whose secretions enter 

 the lumen and join the sperm. The epithelium rests on a connec- 

 tive-tissue sheath encircled by scattered smooth muscle cells in the 

 smallest ducts and a definite coat in the vas deferens. Surrounding 

 the ducts peripherally is a vascular fibroelastic connective tissue 

 which becomes more })rominent as the size of the duct increases. 



MALE REPRODUCTIVE SYSTEM OF FISHES. 



In elasmobranchs the testes are ovoid or cylindrical bodies. The 

 mesonephros is the functional kidney, and in the male the anterior 

 end of it degenerates so far as its urinary function is concerned, 

 and its ducts establish connections with the tubules of the testis 

 during development. Some of the embryonic mesonephric tubules 

 of the anterior end form a much-coiled tube, the epididymis, through 

 which sperm pass from the testis to the mesonephric, or Wolffian, 

 duct, which serves to conduct both urine and sperm to the cloaca. 

 In some cases the kidneys empty by special urinary ducts into a 

 sort of urogenital sinus from which a papilla, the urogenital ])a])illa 

 extends into the cloaca. The ])osterior ends of the two Wolffian 

 ducts are enlarged and act as sperm reservoirs during the l)reeding 

 season. 



