380 



Vertehrata. 



of numerous marine forms {e.g., the Cod), float at the surface of 

 the water ; others are deposited at the bottom ; or are attached 

 to water plants [e.g., the Herring). In the Selachians they are 



enclosed in a horny capsule, 

 which is often flattened and 

 quadrangular with the 

 corners drawn out into 

 threads. Some Fish are 

 viviparous {e.g., most 

 Selachians), and develop- 

 ment takes place in a 

 widened portion of the 

 oviduct (uterus), which 

 is provided with glomerular 

 vascular folds ; also some 

 Teleosteans whose eggs 

 develop in the cavity of the 

 ovary {e.g., the viviparous 

 Blenny). In some few 

 forms there is a special 

 arrangement for the pro- 

 tection of the eggs and 

 brood ; the males of the 

 Stickleback (and of various 

 other Teleostei) build nests, 

 in which the eggs are 

 hatched ; the males of the 

 Pipe-fish carry the eggs and sometimes also the brood about 

 with them, firmly attached to the abdomen, or enclosed in special 

 folds of the skin. This is the case also in various Fish occurring 

 abroad. More rarely the eggs are protected in the same way by 

 the female. 



Fig. 311. Young Pike; ^ just hatched, B, B' 

 eleven days old, C and D still older. In A the tail 

 is still staraight, in C and D markedly heterooeral. 

 a anal fin, c chorda, d dorsal-, p pectoral-, -ia caudal- 

 fin, X anus. — After Sundevall. 



Fig. 312. Larva of a Fish {Trachypterus) which, in the adult, is extraordinarily long, 

 ribbon-like, and without the fin filaments. 



