VERTEBRATA 149 



jaws are complete, and the gills are comblike or tufted, 

 and covered by an operculum. The tail is homocercal 

 except in the "ganoids," as the sturgeon and garpike, 

 in which it is heterocercal or unevenly lobed ; the other 

 fins are variable in number and position. In the soft- 

 finned fishes, the ventrals are absent, as in the eels ; or 

 attached to the abdomen, as in the salmons, herrings, 



FIG. 123. Thornback (Rafa clavata). European seas. 



pikes, and carps; or placed under the throat, as in the 

 cod, haddock, and flounder. In the spiny-finned fishes, 

 the ventrals are generally under or in front of the pec- 

 torals, and the scales ctenoid, as in the perches, mullets, 

 and mackerels. 



The so-called "ganoids" have the body covered with 

 enameled scales or bony plates. 



