276 



COLLEGE ZOOLOGY 



Class V. Arachnida. Examples: scorpion (Fig. 318), spider 

 (Fig. 313), mite (Fig. 322), king-crab (Fig. 327). 



2. Class I. Crustacea 



a. The Crayfish — Cambarus 



The crayfish is abundant both in this country and in Europe. 

 In the eastern United States Cambarus affinis is common. 

 Cambarus virilis is plentiful in the Middle states. The European 

 crayfish is Astacus (Potomobius) fluviatilis. The anatomy and 

 physiology of these three species as well as of the lobster agree 



except in minor de- 

 tails, and the fol- 

 lowing account may 

 be used as a de- 

 scription of any of 

 them. 



Crayfishes usu- 

 ally hide by day un- 

 der rocks or logs at 

 the bottom of ponds 

 and streams. They 

 may be captured by 

 hand, with a net, or 

 with a string baited 

 Fig. 200. -Transverse section throug hi the ab- withapie ceof meat, 

 domen 01 the crayfish. DA, dorsal abdominal f 



artery; EM, extensor muscles of the abdomen; They thrive in an 

 EP, epimeron; FM, flexor muscles of abdomen; _:.,„, anf l their 



M, muscles of appendage; N, endopodite; NG, nerve aquarium, anQtneir 

 ganglion; P, protopodite ; PL, pleuron, PR, intes- entire life-history 

 tine; S, sternum; T, tergum; V, ventral abdominal , nWrved 



artery; X, exopodite. (From Marshall and Hurst.) ma y De 00berVCU 



in the laboratory. 

 The yearly decrease in the number of lobsters available for 

 food, and the steadily increasing demand for crayfishes, will 

 undoubtedly soon make it worth while to raise the latter for 

 market. 



