CHAPTER IV 



THE CRAYFISH {Cambarus sp.) 



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 lobster 

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

 Asiacus.) 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 in- 

 jected by the teacher for the study of the circulatory system. A watery 

 solution of coloring matter or, better, of an injecting mass of gelatine 

 (see Appendix I) is injected into the heart through the needle of a hypo- 

 dermic syringe. For the purpose of injecting, a small bit of the shell may 

 be removed from the cephalothorax above the heart. Specimens which 

 are to be kept for some time should be placed in alcohol or 4% formalin. 



External structure (fig. 10). — 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 exo-skeleton, 

 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 composed of an 

 anterior part, the cephalothorax, and a posterior part, the 

 abdomen. The cephalothorax is covered above and on the 

 sides by the carapace, which is divided into parts correspond- 

 ing to the head and thorax of the toad by the transverse 



aS 



