PART IV. INVERTEBRATA. 



CHAPTER XXIII. THE CRAYFISH. 

 (Astacus fluviatilis.) 



1. Mode of Life, The crayfish is found in England in 

 those rivers which, flowing over chalk or limestone, contain 

 a considerable amount of calcium carbonate in their water. 

 Compared with its companion in the same streams the 

 fresh-water mussel it is a highly-developed animal. In- 



A&STAt/Af 



&WCMOSTCC/TC 



Fig. 148. THE CRAYFISH. 

 Dorsal view. (After Huxley.) 



stead of passively feeding on diatoms and the like, it is active 

 and carnivorous (or rather omnivorous), burrowing holes in 

 the river-banks, in which it lies in wait for prey. At night 

 it sallies forth to crawl over the bottom. It has well 

 developed eyes and olfactory organs by which to recognize 

 prey or enemies ; its large pincers serve as efficient weapons 

 of attack or defence; and it can jerk itself backwards 

 through the water by the sudden flexion of the " tail " 



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