CHAPTER IV 

 THE CRAYFISH (Camdarus sp.) 



LABORATORY EXERCISE 



TECHNICAL NOTE. The crayfish, or crawfish, is found in most of 

 the fresh-water ponds and streams of the United States. (It is not 

 found east of the Hoosatonic River, Mass. In this region the lob- 

 ster may be used. On the Pacific coast the crayfishes belong to the 

 genus Astacus.} Crayfishes may be taken by a net baited with dead 

 fish, or they may be caught in a trap made from a box with ends 

 which open in, and baited with dead fish or animal refuse of any 

 sort. This box should be placed in a pond or stream frequented 

 by crayfish. If possible the student should study the living animal 

 and observe its habits. Crayfish which are to be kept alive should be 

 placed in a moist chamber in a cool place. They will keep for a 

 longer time in a moist chamber than in water. Some fresh specimens 

 should be injected by the teacher for the study of the circulatory 

 system. A watery solution of coloring matter or, better, of an in- 

 iecting mass of gelatine (see p. 451) is injected into the heart 

 through the needle of a hypodermic syringe. For the purpose of 

 injecting, a small bit of the shell may be removed from the cephalo- 

 thorax above the heart. Specimens which are to be kept for some 

 time should be placed in alcohol or 4^ formalin. 



External structure (fig. 3). Place a specimen in a 

 pan for study. Note that the body, which of course differs 

 much in shape from that of the toad, is also unlike that of 

 the toad in being covered by a hard calcareous cxoskclcton, 

 which acts as a covering for the soft parts and also as a 

 place of attachment for the muscles, just as the internal 

 skeleton does in the case of the toad. The body is com- 

 posed of an anterior part, the cephalotJiorax, and a 

 posterior part, the abdomen. The cephalothorax is covered 

 above and on the sides by the carapace, which is divided 

 into parts corresponding to the head and thorax of the 



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