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 Mullerian 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 Mullerian duct, but the homology is uncertain. If correct, then the anterior part of the duct is a Wolffian duct, from which a Mullerian 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 in 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, Lepidostens, 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 Elasmobranchii, e.g. Acanthias, ScyIlium, etc. For the supra-renal capsules see p. 354, ante.
Occasional hermaphroditism has been observed in Cyprinoids, the Mackerel (Scomber), Herring (Clupea harengus), etc. 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 Physostomi. In the latter they are conveyed outwards by the abdominal pore or pores; in Ganoidei by the supposed Miillerian ducts; in the other three orders by Miillerian ducts or oviducts proper. These have in Elas-mobranchii a common internal median aperture, a narrow ciliated duct, a nidamental gland which secretes a shell and the albumen of the egg, and is largest in the oviparous genera, and a dilated posterior part or uterus, in which the ova develope in viviparous species.
The oviducts are convoluted in Dipnoi, and their walls glandular. In Ceratodus the ova are laid in strings imbedded in albumen. The ovaries of the Muraenidae are platelike bands; of Salmonidae lamellate; in other Teleostei saccular, the ova being produced by a small lateral streak on one wall, e. g. Ophrydium barbatum, by processes of the wall, e. g. Lophobranchii or by lamellae transverse, e. g. Clupea harengus, or longitudinal, e. g. Zeus faber. The sticky coat of the ova appears to be formed from the follicle cells.
The testis is saccular only in the Teleostean Syngnathus acus; it is composed in all other Fish of tubuli seminiferi. The sperm is conveyed by vasa efferentia to the mesonephros in Elasmobranchii, Holocephali, chon-drostean Ganoidei and Lepidosteus. It appears to be shed into the coelome in Dipnoi, and is thence conveyed away either by the abdominal pores or by Mullerian ducts, which are present; the latter may be the case with Polypterus and Amia, as it was once supposed to be with other Ganoids. The ducts in Teleostei are continuous with the gland, as in the female, except in Muraenidae, where, though they are present, the sperm is shed into the coelome, whence it is conveyed away by the single abdominal pore. The ducts are often dilated terminally, or furnished with vesiculae seminales. The Miillerian ducts open in Elasmobranchii and Dipnoi into the cloaca dorsally to the rectum; in Holocephali externally between the anus and urinary apertures. For Ganoidei and Teleostei, see p. 427.
Copulatory organs (= pterygopodia) are developed in connection with the metapterygium of the hind-limb in Elasmobranchii and Holocephali. A cartilaginous skeleton supports a deep groove, into which opens a saccular gland in Sharks and Holocephali, a compound tubular gland in Rays. Sperm has been found in the sac in some Sharks and the Holocephali, Dilator and flexor muscles are connected with the apparatus. Impregnation is internal, as it must be in viviparous Teleostei (infra). The sperm 'milt' in other Fish is shed over the ova after they are laid.
The majority of Sharks (except e. g. Scyllidae, Scylliolamnidae, Ces-tracion) and the Torpedo among the Rays, certain Teleostei (many Blen-nidae and Cyprinodontidae) are viviparous. The Teleosteans in question retain the ova in the ovary, the Elasmobranchii in the uterine portion of the oviduct; and in some instances (Mustelus laevis, Carcharias glaucus) the yolk-sac is thrown into folds, which fit into corresponding depressions of the vascular uterine walls, forming a kind of placenta. Among Teleostei the female Aspredo (Siluroidei) carries the ova attached to the soft ventral skin; Solenostoma (Lophobranchii) in a pouch between the ventral fins, and formed partly by them; the male Syngnathidae (Lophobranchii) carry them in a sub-caudal pouch; and in some Siluroidei, e. g. Arius, within the pharynx1. The egg-shell in oviparous Elasmobranchii is chitinoid, with an aperture at one end; usually oblong, with the corners produced into processes, which are often tendril-like2. The zona radiata in Teleostei, and the ovular membranes in other Fish, are perforated by one or more micropyles. The ovum of Elasmobranchii is very large; of Teleostei, with one large or several smaller yolk-spherules; of Acipenser, deeply pigmented.