PISCES 



243 



leave the water and sail for several hundred yards before 

 alighting. The great majority of fishes are strictly gill 

 breathers, but there are also some exceptions in this in- 

 stance. The dipncjans are able to breathe either through 

 gills, or respire air directly by means of lungs. Some other 

 fishes gulp in air, and breathe through the lining of the 

 throat or intestine. 



Breeding habits of fishes are highly variable and often 

 show extreme adaptation. A cod may lay over nine million 

 eggs, which float at the surface of the ocean and receive no 

 care. The male gaff-topsa'1-catfish carries the eggs laid by 



A B 



FIG. 96. Fish nests. A, stickleback; B, dogfish. 



the female in his mouth until after they hatch, and takes no 

 food for ninety days. The male pipefish obtains eggs from 

 a female and carries them in a pouch in his belly until after 

 they hatch. In some species of sticklebacks the male con- 

 structs a nest (Fig. 96, A). In this he induces a female to 

 lay eggs, and watches them with great care. Many basses 

 and sunfishes make " nests" by clearing a shallow basin on 

 the bottom in which eggs are deposited. 



Some fishes carry on extensive seasonal migrations. The 

 salmon, shad, sturgeon, alewife, and striped bass spend most 

 of their lives in the ocean, but enter rivers to breed. The 



