214 



MANUAL OF ZOOLOGY 



SECT. 



being divided into series of movable segments which are 

 termed \hepodomeres. 



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

 regions an anterior, the cephalothorax (cth), which is 

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

 the abdomen (at>), which is divided into distinct segments, 

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



FIG. 123. Astacus fluviatilis, side view of male, a^, antennule; a%, antenna; 

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

 pede; 9, first leg;-/o-/j, remaining legs; ig, uropod; XIV, first abdominal 

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



A natomy. ) 



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. 



