362 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



known in but few species, formed in one species from the ventral fin, in another 

 by the haemal spine of a caudal vertebra, and in a third by an outgrowth behind 

 the anus. 



In the male the testes are simple or lobulated. Internally each testis con- 

 sists of radial chambers of varying shape which are connected with a complicated 

 system of tubules leading to the vas deferens, which runs back to open into the 

 hinder end of the Wolffian duct or to open independently to the exterior (fig. 

 383, go). 



Hermaphroditism is rare among teleosts. It occurs commonly among the 

 species of Serranus and Chrysophrys, and has been observed with specimens of 

 cod, mackerel and herring. 



Interrenal organs are known in the bony fishes, scattered in or on the ventral 

 surface of the mesonephros (Stannius's corpuscles). Suprarenals have been 

 described in the wall of the cardinal vein, but this is uncertain. 



DIPNOI. — In Ceratodus there are two pronephric tubules, that of the third 

 somite being complete, that of the fourth rudimentary. The glomerulus lies 



Fig. 383. — Hinder part of urogenital organs of male pike, Esox lucius, after Good- 

 rich, a, anus; ab, air bladder; ao, aorta; cv, cardinal vein; d, Wolffian duct; g, genital 

 duct; go, genital opening; i, intestine; pc, postcardinal vein; t, testis; ub, urinary bladder; 

 uo, urinary opening; m, mesonephros; cv, caudal vein. 



beside the open nephrostome. The mesonephros is at first strongly metameric. 

 There are no nephrostomes in the adult and none appear at any time in Lepido- 

 siren. The adult mesonephros is widest behind, but the relations of the efferent 

 ductules of the male are differently arranged in the separate genera, as mentioned 

 above (p. 350). 



The reproductive organs are apparently more like those of elasmobranchs. 

 The oviducts resemble, at least in structure, Miillerian ducts, and have their 

 ostia far forward near the heart. These tubes, like those of the amphibia, 

 secrete a gelatinous substance around the eggs. The ducts of the two sides 

 unite before emptying at the tip of the genital papilla into the cloaca. The 

 same ducts are retained in the male Ceratodus and to a less extent in the other 

 genera. 



The gonads are elongate. The testes are enveloped, together with the 

 mesonephroi, in a lymphoidal tissue rich in fat. The sperm passes into a longi- 

 tudinal tubule (fig. 373) and from this by one (Protopterus) or several efferent 



