dorsal side there is thick and highly calcified exoskeleton, 

 but the ventral wall is membranous. 



The dorsal wall consists of a median portion — the 

 tergum (text fig. 1, t.) — which is continued into two 

 broad lateral portions — the pleura. The median ventral 

 wall is known as the sternum, and from each of the outer 

 portions of the sternum arises an appendage. Between 

 the point of attachment of each appendage and the 

 pleuron the ventral wall is known as the epimeron. 



■t. 



Fig. 1. — Diagrammatic section through female abdomen. 



t.= tergum. m.a. =muscles of abdominal 



p. = pleuron. appendage. 



s. = sternum. h.g. =hind gut. 



e. = epimeron. pr. =protopodite. 



e.m. = extensor muscles of abdomen, ex. = exopodite. 

 /. m. = flexor muscles of abdomen. en. = endopodite. 



The segment is connected with the two neighbouring 

 segments by a thin uncalcified part of the exoskeleton — 

 the arthrodial membrane. This allows of free movement 

 between the segments. Each segment articulates with 

 the one in front by means of a pair of hinges placed at 

 the outer and anterior part of the pleuron at each side. 



The appendages will be described in detail later. 



Cephalothorax. 



1. Carapace. 



The terga and pleura of the cephalothorax are fused 

 to form the large Carapace. This is a broad shield the 

 width of which is about 1^ times as great as the length. 



