PARTS OF ANIMALS, IV. vii.-viii. 



water to drink, which is their way of taking nourish- 

 ment. All of them possess a head, but except for 

 the part Λvhich takes in the food none of the other 

 parts has a special name. 



VIII. All the Crustacea can walk on land as well as (c) Cru> 

 swim ; and hence they all have numerous feet. There "*"*" 

 are four main groups of Crustacea, called (l) Carabi ; 

 (2) Astaci; (3) Carides; and (4) Carcini." Each of 

 these contains several species which differ not only 

 in shape, but also in size, and that considerably, for 

 some species are large, others extremely small. The 

 Carcinoid and the Caraboid Crustacea resemble each 

 other, in both having claAvs. These claws are not for 

 the sake of locomotion, but serve instead of hands, 

 for catching and holding ; and that is why they bend 

 in an opposite direction to the feet, which bend and 

 tAvist toward the concave side, while the claws bend 

 toward the convex side. This makes the claws 

 serviceable for catching hold of the food and convey- 

 ing it to the mouth. 



The tΛvo groups, Carabi and Carcini, differ in that 

 the former have a tail and the latter have not. The 

 Carabi find a tail useful because they are swimmers : 

 they propel themselves with it as though with oars, 

 A tail A\Ould be useless to the Carcini, which spend 

 their lives near the land and creep into holes and 

 crannies. Those that live out at sea and move about 

 but little, and OΛve their safety to their shelly exterior, i 

 have for these reasons feet which are considerably less 

 effective for locomotion : examples of this are the 



» Roughly, these four divisions may be represented by our 

 own groups, thus : (1) lobsters ; (2) crajrfish ; (3) prawns and 

 shrimps ; (4) crabs. 



351 



