TETRADECAPODA. 



Contrasted to the Decapods are the fourteen-footed or 

 Tetradecapodous forms, of which the sow-bug is one type. 

 In these we can distinguish clearly head, thorax, and 

 abdomen, the joints of the thorax being freely movable on 

 each other. The eyes are not placed upon movable stalks, 

 but are scarcely elevated above the general surface of the 

 head. Most of these forms are marine; a few live in fresh 

 water, and still fewer, like the sow-bugs and pill-bugs, upon 

 the land. All are small, those which reach two inches in 

 length being the veritable giants among the group. 



There are two subdivisions of Tetradecapods : Isopoda 

 and Amphipoda. 



In the Isopoda the body is depressed, as in the sow-bug, 

 and the gills are borne under the abdomen. Most of the 

 Isopoda feed upon decaying matter, but some have become 

 parasites upon other animals, and have consequently so 

 changed their appearance that one knowing only the adult 

 would never regard them as Isopods at all. But the young 

 settle the question, since before they begin their parasitic 

 life they are regular Isopods. 



In the Amphipods the body is compressed from side to 

 side, and the gills are borne on the thoracic region between 

 the legs. These forms are familiar to all visitors to the 

 shore under the common name of " beach-fleas/' a name 

 which those forms living under dried seaweed, etc., have 

 won for themselves through their leaping powers. Others 



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