PISCES. 



427 



the coelome. In all cases they lie subvertebrally. The metanephros of 

 Elasmobranckii is more or less lobulated. The duct lies sometimes in the 

 substance of the gland in Teleostei, at its outer margin in Ganoidei, on the 

 ventral surface in Dipnoi, and the several ducts (rarely a single duct) in 

 Elasmobranckii proceed from its inner border. The duct in Teleostei is 

 probably an archinephric duct : in Elasmobranchii that of the mesonephric 

 region is a true mesonephric (or Wolffian) duct, from which a Miillerian 

 duct has been split off in development, as is probably the case also in 

 Dipnoi. The Ganoidei present a difficulty. The renal duct has a second 

 duct opening into it near its centre, as well as into the coelome, which is 

 usually regarded as a Miillerian duct, but the homology is uncertain. If 

 correct, then the anterior part of the duct is a Wolffian duct, from which a 

 Miillerian duct has been split off, and the posterior part is an undivided 

 archinephric duct. The ducts, archinephric or mesonephric, fuse terminally, 

 and the fused portion is dilated in Elasmobranchii ; provided with a lateral 

 outgrowth on each side in Amia ; or a median outgrowth (urinary bladder), 

 sometimes of great size, in Teleostei. The fused portion is functionally a 

 urogenital sinus in both sexes among Ganoidei and in the male Elasmo- 

 branch ; and in the latter it receives the metanephric ducts or ureters which 

 in the female open into the lower ends of the mesonephric ducts before 

 they fuse. The ducts finally open into the cloaca vn. Elasmobranchii and 

 Dipnoi, externally behind the anus in Ganoidei and in Teleostei, in the latter 

 either into a sinus, common also to the genital ducts, or else separately 

 behind the genital opening, as is the case also in Holocephali. Some 

 Teleosteans, e. g. Gobies, Blennies, have a long urogenital papilla. Pro- 

 topterus has a so-called urinary bladder opening into the cloaca between 

 the rectum and the sexual ducts. Peculiarities are the conversion of the 

 anterior part of the mesonephros in Acipenser, Lepidosteus, many Teleostei, 

 into adenoid tissue, into which the kidney duct does not extend, and the 

 retention of nephrostomata, variable in size and number in many Elasmo- 

 branchii, e.g. Acanthias, Scy Ilium, &c. For the supra-renal capsules see p. 

 354, ante. 



Occasional hermaphroditism has been observed in Cyprinoids, the 

 Mackerel {Scomber), Herring (Clupea harengus), &c. Among Teleostei 

 Acanthopteri a testis is constantly found imbedded in the wall of the ovary 

 in Chrysophrys and Serranus, and the last-named Fish is said to be self- 

 impregnating. The glands are small when immature, and are typically 

 paired. A single ovary is found, however, in Scyllidae, Galeidae, Car- 

 charidae among Elasmobranchii, and a few Teleostei', a single testis in a 

 very few of the latter. The ova are carried away in Lepidosteus and 

 Teleostei with one exception, by ducts continuous with the ovarian capsule 

 (p. 89). They are shed into the coelome in Elasmobranchii, Holocephali, 

 Dipnoi, Ganoidei, in the Salmonidae and Muraenidae among Teleostei 



