210 SUB-CLASS (AND ORDER) TELEOSTEI. 



continuous with the short duct which either opens in the same 

 position as in the female, or joins the ureter, so that there 

 is a median porus urogenitolis behind the anus. 



In the viviparous forms fertilisation is effected by an in- 

 tromittent organ, which is usually formed by the urogenital 

 papilla. A few Teleosteans (Serranus, etc.) are hermaphrodite. 



The ova fall into the body-cavity and escape by porelike oviducts in the 

 Galaxiidae, Hyodontidae, Nolopteridae, Muraenidae and Salmonidae. 



In Fierasfer there is said to be a pronephros in the adult, and the pos- 

 terior part of the kidney is not developed. 



The ova are always provided with soft shells and vary con- 

 siderably in size ; amongst the largest are those of Gymnarchus 

 (10 mm.) and of Arms (5 to 18 mm.). They may be deposited 

 singly (salmon, trout, etc.), or they may be agglutinated to- 

 gether by a substance secreted by the walls of the oviduct. In 

 freshwater forms they either adhere to some foreign body or are 

 deposited in nests ; in marine forms they are either attached to 

 foreign bodies or float freely in the surface waters of the ocean, 

 or sink to the bottom as in the herring. Most fishes breed once a 

 year at a definite period, but some breed more than once, and 

 in some the breeding period is much prolonged as in the cod 

 and herring. 



Care of the brood by the female is often found (Aspredo, 

 Solenostoma, Cichlidae, see systematic part) ; in the male it is 

 more frequent (by nests in Gymnarchus,* Heterotis, Coitus, 

 Gafttrosteus, Cyclopterus, Antennarius, Ophiocephalus, Callichthys, 

 etc. ; in Arius the eggs are carried in the pharynx of the 

 male, in Lophobranchs in a pouch on the abdomen). 



The segmentation is meroblastic and the germinal layers arise 

 by delamination. The cerebro-spinal cord is formed as a solid 

 keel-like thickening of the ectoderm,which subsequently becomes 

 hollow. The young are hatched at an early stage arid undergo 

 the remainder of their development as larvae. The larvae have 

 a pronephros and considerable remains of the yolk-sac. The 

 Teleostean pronephros is characteristic, in that the portion of 

 the body-cavity containing the glomerulus is quite cut off from 

 the rest and is in relation with the pronephric duct by one body- 

 cavity opening only. 



* Budgett, Breeding Habits of some W. African Fishes, etc., Trans. 

 Zool. Soc., 16, 1901, p 115. 



