568 ANATOMY OF VERTEBRATES. 



CHAPTER XL 



GENERATIVE SYSTEM OF II^EMATOCllYA. 



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 f vas deferens,' next of a vesicula seminalis 

 and prostate, afterwards of an intromittent 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)* 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 serdus 

 covering, into a short and simple sperm-duct, or 6 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, prop. no. 2373. 2 Ib. p. 49, prep. no. 2378. 



