GENERATIVE SYSTEM OF FISHES. 



287 



Renal and Male Organs : 

 Trigla lyra, Carus. 



whicli is continued from the posterior end of the gland, with its 

 serous covering, into a short and simple ' vas deferens,' which opens 

 usually into or receives the urethral prolongation of the urinary- 

 bladder. In the Gurnard the testes {Jig. 72. a) are distinct from 

 each other, but their ' vasa deferentia' almost im- 

 mediately unite into a common duct, which joins 

 the urethra (c) behind the rectum (Ji), and ter- 

 minates at the outlet {g). In the Salmon and 

 the Herring, the ' vasa deferentia ' do not unite 

 together until near their termination in the 

 urethra. In the Cod and the Bull-head {Cotti(s) 

 the common portion of the efferent duct is much 

 dilated : it forms a saccular seminal reservoir 

 in the Sole. The canal common to the ureter 

 and vas deferens is of great length in the Stur- 

 geon : a valve prevents the regurgitation of the 

 urine into the spermatic duct. The urethra is 

 usually produced into a papilla, which pro- 

 jects conspicuously from the back part of the cloaca in the vi- 

 viparous Poecilia, Anableps, and Blenny : it is large also in the 

 Lump-fish. The testes are almost entirely extra-abdominal in the 

 Flounder and some other Pleuronectidce, extending backwards into a 

 kind of concealed scrotum between the integuments and muscles on 

 each side above the anal fin. The testes differ much in foi'm in dif- 

 ferent Osseous Fishes, but are remarkable in all for their enormous 

 seasonal increase : when fully developed they are commonly known 

 as the 'milt' or 'soft roe.* In the Pipe-fishes (S^/ng?iathi) they 

 present the form of two simple elongated straight tubes (prep. 2375.). 

 In the Lump-fishes (^Cyclopteri) they are divided by incisions into 

 lobes : in the Cod a vast extent of the vascular surface of the glan- 

 dular substance is packed into a small compass, by being disposed in 

 convolutions upon the edge of the ' mesorchium.' The primitive 

 spermatic cells, which are persistent in the Cyclostomes, have coa- 

 lesced 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.* 



In the Plagiostomes the testes {fig. 73. «) are always distinct 

 from one another, and usually of a circumscribed compact form, si- 

 tuated far forwards in the abdominal cavity. They have a proper 



* cxx. p. 105. pi. XV. fig. 7. ill the Shad. 



