chap, in.] CRUSTACEA. 67 



exoskeleton of the separate metameres, and the 

 Malacostraca, which were so called because their 

 covering is soft as compared with the hard shell of 

 the oyster or the snail. In both divisions we find 

 members which .have become parasitic in habit, and 



Fig. 27. The Common Prawn (Palcemon serratus). 



in which, consequently the characteristics of ar- 

 thropod organisation are more or less modified and 

 obscured. 



In the Entomostraca we never have more than 

 three pairs of appendages converted into Onatliites, 

 or jaws; the appendages behind the genital orifices 

 never carry appendages (Fig. 26; 5), and the young 

 nearly always make their appearance as unsegmented 

 larvae with two or three pairs of appendages, of 

 which two are constantly biramose (Naiiplius 

 larvae) (Fig. 26 : 4, 56, 6). 



1. The Brancliiopoda have, as their name 



