ANATOMY OF VERTEBRATES. 



I 



('II AFTER XI. 



GENERATIVE SYSTEM OF H^EMATOCRYA. 



§ 106. Male Organs of Fishes. — All Fishes are dioecious, or of 



distinct sex. The male parts of generation present a progressive 



gradation of complexity from the essential gland, or testis, as a 



single organ distinguishable only by microscopic examination of 



its contents from an ovarium, to a more definite and concentrated 



form of testis with complete bipartition ; then to the developement 



of a proper duct or ' vas deferens,' next of a vesicula seminalis 



and prostate, afterwards of an intromitteiit organ, and finally of 



superadded ' claspers,' or mechanical instruments for retention 



of the female in coitu. In Petromyzon marinus the testis is a 



long thin plate, disposed in the form of a series of folds, closely 



attached by a duplicature of the peritoneum to the median line of 



the back of the abdomen, between the kidneys ; the extension of 



the overlapping oblique folds to the right and left, of the line of 



attachment feebly indicates the duplex character of the gland. 1 



Its tissue consists of small spherical cells filled with spermatozoa, 



fig. 402. These escape, by dehiscence of the cells and rupture 



of the peritoneal covering, into the abdominal cavity, and are 



expelled by reciprocal pressure of the intertwined sexes from the 



peritoneal outlets at the cloaca. The Eel closely resembles the 



Lamprey in the general form and condition of the male organs ; 



but the right and left sides of the plicated testis are more distinct, 



and the spermatic cells are more numerous and minute. 



The Sand-Eel (Ammodytes) q has a single testis, compacted into 

 an elongated triedral form, and impressed by a median longitudinal 

 fissure : it usually inclines a little to the right side. In the Perch 

 the single testis inclines to the left : in the Blenny and the Loach 

 it lies in the middle line. In these osseous fishes the glandular 

 part of the testis is inclosed in a proper fibrous capsule, which is 

 continued from the posterior end of the gland, with its serous 

 covering, into a short and simple sperm-duct, or ' vas deferens,' 

 which opens usually into, or receives, the urethral prolongation 

 of the urinary bladder. In the Gurnard the testes, fig. 378, a, 



1 xx. vol. iv. p. 48, prep. no. 2373. " lb. p. 49, prep. no. 2378. 



