CHAPTER X 

 THE CRAYFISH AND OTHER CRUSTACEA 



It is a convenient and common practice to study the 

 crayfish as a type of the Crustacea, especially ever since 

 Professor Huxley so used it, and wrote his celebrated 

 volume on this animal which can be heartily recommended 

 to every student of biology. The body of the crayfish 

 is covered by a chitinous external skeleton as in insects, 

 but it is hardened by deposits of lime salts, except at 

 the joints where it remains thin and flexible. The head 

 and thorax are fused into one piece, the cephalothorax, 

 which is covered dorsally and at the sides by a sort of 

 foTd called the carapace. Anteriorly the carapace is 

 prolonged into the rostrum or beak. The part behind 

 the cephalothorax is the abdomen and consists of seven 

 freely movable segments or somites, the terminal one 

 being called the telson. 



The eyes of the crayfish are compound and situated 

 on movable stalks. There are two pairs of antennae; 

 the first pair has two slender flagella, the outer one of 

 which bears minute, club-shaped bodies which are organs 

 of smell. The long second antennae are mainly used as 

 organs of touch; the first segment, however, contains the 

 opening of the "green gland'' or organ of excretion. 



The crayfish is furnished with six pairs of mouth parts, 

 the first of which, the mandibles, are stout organs well 

 adapted for crushing food. The two following pairs are 

 the maxilla, and these are followed by three larger pairs 

 of appendages called the maxillipeds. The first pair of 



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