6o6 



PHYLUM CHORDATA : CLASS PISCES — FISHES 



The male organs or testes lie on each side of the cardinal 

 sinus, moored by a fold of peritoneum. Spermatozoa 

 pass from the testis by vasa efferentia into a tube sur- 

 rounded anteriorly by epididymis. The tube of the 

 epididymis is continued into the vas deferens, which 



Fig. 343. — Elasmobranch development. — After Balfour. 



Uppennost figure shows blastoderm at an early stage. Ep., Epiblast 



or ectoderm ; sg.c, segmentation cavity ; n., yolk-nuclei. 

 Middle figure shows the invagination which forms the gut. x., 



Blastopore ; g., archenteron. Mesoderm dark. 

 Lowest figure, a longitudinal section at a later stage. Ep., 



Epiblast or ectoderm ; n.c, neural canal ; ne.c, neurenteric 



canal ; g., gut ; n., notochord. Mesoderm dark. 



is dilated posteriorly into a seminal vesicle and an adjacent 

 sperm-sac. Finally, the two vasa deferentia open into the 

 urinogenital sinus, whence the spermatozoa pass into the 

 cloaca. Thence, in copulation, they pass into the complex 

 " claspers " of the male, which are said to be inserted 

 into the cloaca of the female. 



The female organs or ovaries lie on each side of the 



