570 



ANATOMY OF VERTEBRATES. 



380 



pass, by being disposed in convolutions upon the edge of the 

 ' mesorchium.' The primitive spermatic cells, which are per- 

 sistent in the Cyclostomes, have coalesced into tubes (tubuli 

 seminiferi) in Osseous Fishes ; the tubes open at one end in the 

 wide and sometimes saccular commencement of the vas deferens, 

 and terminate at the other, either by blind free extremities or 



by reticulate anastomoses. 1 In the Herring, Shad, 

 and other Clupeoids, the secerning tubes ramify 

 and anastomose in the substance of the testicle, 

 and from this plexus, fig. 379, the initial casca 

 are prolonged to the surface of the gland, where 

 their obtuse blind ends give a granulated appear- 

 ance to the exterior. 



In the Plagiostomes the testes, figs. 352, k, 

 380, , are always distinct from one another, and 

 usually of a circumscribed compact form, situated 

 far forward in the abdominal cavity. They have 

 a proper capsule, or ' tunica albuginea,' and a 

 peritoneal covering ; the capsule sends many ( septa' 

 into the substance of the gland, and the lobes thus 

 formed consist chiefly of the tubuli testis, and 

 their expanded cell-like extremities, filled with 

 the spermatozoa : the convolutions of the f tubuli ' 

 are plainly discernible in the portion of the testis 

 of the Basking Shark (Selache maxima) preserved 

 j n ^Q Hunteriaii Museum. London, prep. no. 



t * 



2396, A. 2 Numerous ( vasa efferentia' convey 

 the f semen ' to the beginning of the f vas deferens,' 3 which forms 

 a large ( epididymis,' fig. 380, b, by its manifold convolutions. 

 These gradually decrease as the duct, ib. e, approaches the cloaca, 

 when it becomes straight, and expands into an elongated reservoir, 

 ib. f, the mucous surface of which is commonly increased by 

 numerous transverse plica3, as in Spinax and Selache. Behind 

 the termination of the rectum the ' vasa deferentia ' suddenly 

 diminish, approximate, communicate with the ureters, and ter- 

 minate upon the cloacal penis, fig. 352, o. This is hardly visible, 

 and the testes are very small, except at the breeding season, in 

 the Piked Dog-fish (Spinax). 



The claspers are present in the Chimaeroid Fishes as well as in 

 the Plagiostomes. They project backward, as appendages to the 

 bases of the anal fins, and are sometimes bent inward at their 

 free extremities, figs. 352, ^, 380, m. Near this part may be 



1 cxxn. p. 105. ' xx. vol. iv. p. 52 



organs, left side: 



Spinax. 



cxxxiv. 



