2QO ELEMENTARY ZOOLOGY. 



development, gradually working their way back to the 

 sea. It is on these migrations of the salmon in the rivers 

 of western America that they are caught and canned for 

 the market. 



Some of the eels are known to generate in the sea and 

 spend their later life in the fresh water. 



FIG. 113. Atlantic salmon (Salmo solar). U. S. Fish Commission. 



Questions on the Figure. What are the names of the various fins 

 shown in the figure? What is the dotted line along the side of the 

 fish? 



300. The Main Types of Fishes. There are two orders 

 of fishes that are important because of their numbers 

 and present development, and two orders that are interest- 

 ing chiefly because of their evolutionary importance. 



The sharks, skates, and saw-fish (elasmobranchs) are 

 fierce and powerful marine fishes. They are of lower 

 development than the next group. The skeleton is often 

 wholly cartilaginous. The mouth is not at the end of 

 the head, but is on the under side. The gills do not have 

 a cover as in the higher .fishes. The two parts of the 

 tail fin are not equal. 



The common bony fishes (teleosts) such as the trout, 



