540 



ZOOLOGY 



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 



Fio. 430^.— Astacus fluviatilus, side view of male, ~a\ antennule ; <fi, antenna ; ah. abdomen ; 

 etk. cephalothorax ; k-ti, gill-cover ; r. rostrum; 8, third maxillipede ; 0, first leg; 10 — 13, 

 remaining legs ; 1!», uropod ; XIV, first abdominal segment ; XIX, sixth abdominal segment. 

 (From Lang's Comparative Anatomy.) 



Fio. 430/?. — Transverse section of abdomen of Crayfish. DA, dorsal abdominal artery; EM, 

 dorsal muscles of the abdomen ; El', space between the plcuron and the appendage; FM, 

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

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

 abdominal artery ; X, exopoditc. (From Parker's Practical Zoology, after Marshall and Hurat. 



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

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

 abdomen (ab), which is divided into distinct segments, movable upon 



