XI 



PHYLUM ARTFTROPODA 



527 



b. The Fresh-water Crayfish (Astacus fluviatilis). 



Antaeus Jluviatilis is common in streams and rivers in England 

 and the -continent of Europe ; allied species occur in Asia and 



PR 



FM 



I'lQ. 437. Astacus fluviatilus, side view of male, a 1 , antennule ; a 2 , antenna ; ab, abdomen; 

 cth. cephalothorax ; l:.d, gill-cover ; r. rostrum ; S, third maxillipede ; 9, first leg ; 10 13, 

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

 (From Lang's Comparative Anatomy.) 



North America ; and fresh-water Crayfishes belonging to other 

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

 found in America, Australia, and New Zealand. 



External Char- 

 acters. The body 

 o f the C r a y fi s h 

 (Fig. 437) is divided 

 into two regions 

 a n anterior, the 

 cephalothorax (cth.), 

 which is un jointed, 

 and is covered by 

 a carapace resem- 

 bling that of Apus, 

 but of smaller pro- 

 portional size ; and 

 a posterior,, the ab- 

 domen (ab), which 

 is divided into dis- 

 tinct segments, 

 movable upon one 

 another in a vertical 

 plane. The cepha- 

 lothorax is again 

 divided into two 



PI 



FIG. 438. Transverse section ul' abdomen of Crayfish. DA 

 dorsal abdominal artery ; EM, dorsal muscles of the abdomen 

 EP, space between the pleuron and the appendage ; FM 

 ventral muscles of the abdomen ; M, muscles of the appendage 

 N, endopodite ; NO, nerve-ganglion ; P, protopodite ; PL, 

 pleuron; PR, hind-gut; S, sternum; T, tergum ; V, ventral 

 abdominal artery ; X, exopodite. (From Parker's Practical 

 Zoology, after Marshall ami Hurst.) 



