XI 



PHYLUM ARTHROPODA 



575 



Other Anomura, such as the Cocoa-nut Crab (Birgus), Hippa, &c., 

 approach the Brachyura in the short, more or less permanently 

 flexed abdomen, but are clearly separated from them by the 

 structure of the head and its appendages. 



In the Brachyura, or true Crabs, we reach the highest degree of 

 specialisation known among the Crustacea. The cephalothorax 



Kni. 475. Cancer pagurus. A, dorsal, B, ventral aspect, ant.l, antennule ; ant.2> 

 antenna ; abd.l, abti.3, abd.7, abdominal segments ; E eye-stalk ; l.l, 1.5, legs ; mxp.3, third 

 maxillipedes. (After Bell.) 



(Fig. 475) is always of great proportional breadth, and is frequently 

 much broader than long. The abdomen, on the other hand, is 

 greatly reduced, its sternal region is uncalcified, and it lies per- 

 manently flexed in a groove on the very broad thoracic sterna, so 



