540 



ZOOLOGY 



SECT. 



genera, but agreeing with Astacus in all essential features, are 

 found in America, Australia, and New Zealand. 



External Characters. The body- of the Crayfish (Fig. 430,^4 

 and B) is divided into two regions an anterior, the cephalothorax 



FIG. 430 A. Astacus fluviatilus, side view of male, a 1 , antennule ; a-, antenna ; ah. abdomen ; 

 cth. cephalothorax ; kd, gill-cover ; r. rostrum ; 8, third maxillipcde ; 'J, first lug ; 10 13, 

 remaining legs ; 19, urqpod ; XIV, first abdominal segment ; XIX, sixth abdominal segment. 

 (From Lang's Comparative Anatomy.) 



EM 



FIG. 430 B. Transverse section of abdomen of Crayfish. DA, dorsal abdominal artery ; EM, 

 dorsal muscles of the abdomen ; EP, space between the pleuron and tho appendage; FM, 

 ventral muscles of the abdomen ; M, muscles of the appendage ; N, endopodite ; NG, nerve- 

 ganglion ; P, protopodite ; PL, pleuron ; PR, hind-gut ; S, siernum ; T, tergum ; V, ventral 

 abdominal artery ; X, exopodite. (From Parker's Practical Zooloyy, after Marshall and Hurst. 



(cth.), which is unjoirited, and is covered by a carapace resembling 

 that of Apus, but of smaller proportional size ; and a posterior, the 

 abdomen (afy, which is divided into distinct segments, movable upon 



