CRUSTACEA. 



329 



and which really consists of fourteen coalescent segments. 

 The cephalothorax is generally covered by a great shield or 

 buckler, which is termed the "carapace" (fig. 194, 1, ca), 

 and which is produced by an enormous development of 

 the dorsal walls of one or two of the cephalic somites. 



Fig. 194. Morphology of Lobster. 1. Lobster with all the appendages, except the 

 terminal swimmerets, removed, and the abdominal somites separated from one another : 

 ca, Carapace ; t, Telson. 2. The third abdominal somite separated : t, Tergum : s, Ster- 

 num ; p, Pleuron ; a, Propodite ; b, Exopodite ; c, Endopodite. 3. One of the last pair 

 of foot-jaws or maxillipedes : e, Epipodite ; g, Gill ; the other letters as before. 



Each segment of the body may be regarded as essentially 

 composed of a convex upper plate, termed the " tergum," 

 which is closed below by a flattefr plate, called the "sternum," 

 the line where the two unite being produced downwards and 



