UROGENITAL ORGANS 359 



with which an oval sperm sac is connected on either side. In the holocephali 

 fig. 379) the epididymal region is separated by a considerable interval from 

 the rest of the mesonephros and forms a large Leydig's gland which secretes the 

 spermatophores. The Miillerian duct is reduced in the male, and frequently 

 is without a lumen; its anterior end may retain a reduced funnel. 



As fertilization is internal in the elasmobranchs, the posterior or inner side 

 of the pelvic fin is specialized for a copulatory organ, by which, even in the late 

 embryo, the sexes can be distinguished. The metapterygium (p. 124) and the 

 basalia connected with it are more or less completely separated from the rest 

 and form the so-called clasper (muripterygiiun), a slender part of the fin. Each 

 clasper is grooved along its medial surface and when the two are inserted in the 

 cloaca of the female the grooves form a tube for the passage of the spermatozoa. 

 The clasper contains a large gland, but its relations to copulation and fertiliza- 

 tion are unknown. 



The interrenals are paired in skates, elsewhere unpaired; they may form a 

 continuous mass (fig. 377) or may be separate bodies between the kidneys, 

 recognizable from their yellow color. The suprarenals are metameric in the 

 sharks, irregularly distributed in the skates, but always in close relations to the 

 sympathetic system, and in their posterior range they may be imbedded in the 

 raesonephroi. 



GANOIDS. — The number of pronephric tubules varies from two (second 

 and fifth postotic somites) in Polypierus, to five or six in Lepidosteus and stur- 

 geons and eight to eleven in Amia. The pronephros degenerates in the adult. 

 The mesonephros has nephrostomes in Amia and the sturgeons. This organ is 

 markedly segmental, and in the sturgeons the anterior part is separated from 

 the rest, while the organs of the two sides are united behind. The urinary ducts 

 are the Wolffian ducts, and the Miillerian ducts of the females enter the urinary 

 bladder. 



In most species the ovaries are band-like and there are oviducts which have 

 broad internal funnels and, as said above, they open to the exterior together 

 with the urinary ducts, a relation which favors the view that they are Miillerian 

 ducts like those of elasmobranchs, but reduced in extent in correlation with the 

 backward extension of the gonads. In Lepidosteus, however, the ovary is 

 saccular as in the teleosts, the eggs passing into the central cavity and then to 

 the exterior by a duct which is apparently but a sterile backward extension of 

 the ovary. The males are more normal, the testes being frequently lobulated 

 and with the regular ductules leading from the testes to the anterior end of the 

 mesonephros (fig. 373) and thence separately or by a common duct into the 

 Wolffian duct. The males of all but Lepidosteus have short funnels like the 

 females, an additional evidence that these are reduced MuUerian ducts. 



TELEOSTS. — In development the pronephros extends over from one to 

 six somites, these having a tendency to form a common chamber and a 

 glomus. Usually the pronephros degenerates, but it persists through life in a 

 few species {Zoarces, Lepadogaster, Fierasfer) and functions in the larval stages 

 in many more. The mesonephros varies in shape. Frequently the organs of 

 the two sides are united behind, less frequently in front, while occasionally there 

 is a cross connexion in the middle; lobes may extend forward from the main 



