15 



THE CRAYFISH AND OTHER 

 ARTHROPODS 



Crayfishes are found in many English rivers, especially in those 

 which rise in chalk or limestone hills. They are little, lobster-like 

 creatures, which make burrows in the river banks. They dislike 

 strong light and during the daytime generally remain in their 

 holes with only their pincers and long feelers projecting. When 

 they come out they crawl stealthily about, searching constantly 

 for their food, which consists of organic matter of any kind, 

 plant or animal, dead or alive, that they are able to seize and 

 break up with their pincers. If danger threatens, they dart 

 backward suddenly and swiftly. They are used for food, especially 

 for garnishing salads, and were formerly caught in large numbers 

 in this country by means of wicker crayfish-pots, but in 1887 

 their numbers were greatly reduced by a disease. The name is 

 also used for a number of related genera in various parts of the 

 world. 



EXTERNAL FEATURES 



The English crayfish, Astacus pallipes (Fig. 132), is about 

 three inches long, and of a dull, greenish colour, which harmonises 

 well with the surroundings in which it lives. A number of other 

 species are found on the Continent. The body of a crayfish is 

 armoured with a thick cuticle. It is segmented, each segment 

 bearing a pair of jointed limbs, but in the front part the segments 

 are fused to form a fore-body or cephalo thorax, where the only 

 conspicuous sign of their existence is the presence of several 

 pairs of limbs, though parts of the armour and certain internal 

 organs are also segment ally arranged. The rest of the body, 

 known as the hind body or abdomen, is more completely seg- 

 mented. At the end of the abdomen is a flat piece known as 

 the telson, on the under side of which the anus opens. The telson 

 bears no limbs, and is divided by an imperfect transverse joint. 

 The armour of each segment of the abdomen consists of a broad 

 back-piece or tergum and a narrow belly-plate or sternum, with 

 a pair of V-shaped prolongations, known as the pleura, joining 

 them at the sides. There are no pleura on the first abdominal 



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