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MANUAL OF ZOOLOGY 



being divided into series of movable segments which are 

 termed the podomeres. 



The body of the crayfish (Fig. 123) is divided into two 

 regions — an anterior, the cephalothorax (elk), which is 

 covered by a broad shield or carapace ; and a posterior, 

 the abdomen (ad), which is divided into distinct segments, 

 movable upon one another in a vertical plane. The cepha- 



FlG. 123. — Astacus fluviatilis , side view of male. a it antennule; a 2 , antenna; 

 ab, abdomen; ctk, cephalothorax; kd t gill-cover; r, rostrum; 8, third maxilli- 

 pede; q, first leg; /o-/j, remaining legs; IQ, uropod; XIV, first abdominal 

 segment ; XIX, sixth abdominal segment. (From Lang's Comparative 

 Anatomy.) 



lothorax is again divided into two regions — an anterior, the 

 head, and a posterior, the thorax — by a transverse depres- 

 sion, the cervical groove. The carapace is developed from 

 the dorsal regions of both head and thorax, and is free only 

 at the sides of the thorax, 1 where it forms a flap or gill-cover 



1 This was the view of Huxley, but it is the opinion of American authors 

 that the carapace is the enlargement of the fused tergites or dorsal region of 

 two head-segments, i.e., the second antennal and mandibular; those of 

 the succeeding cephalothoracic segments being atrophied. — AMERICAN 

 Editor. 



