44 STUDIES OF ANIMAL LIFE. 



E. Appendages of the Abdomen. 



1. The Swimmerets. 



The appendages of the abdomen are called swim- 

 merets. 



a. How many pairs of swimmerets are there ? 



b. Which somites are not provided with swim- 



merets ? 



c. Observe that each swimmeret is made up of the 



following parts, — 



(1) protopod, the stalk ; 



(2) exopod, the outer branch ; 



(3) endopod, the inner branch. 



d. What are the movements of the swimmerets ? 



(Watch crayfishes in water.) 



e. What are the uses of the swimmerets ? 



(Examine a crayfish which is carrying its eggs.) 



2. The Caudal Fin. 



The caudal fin is made up of the seventh somite 



(telson) and the swimmerets of the sixth somite. 

 a. What is the shape of the caudal fin ? 

 h. What is its use ? (Place a crayfish in water and 

 watch it swim.) 



c. How is it used ? 



d. How are the parts of the fin arranged ? 



e. How is it adapted to its work ? 



F. Appendages for Taking Food. 



There are three groups of appendages for taking food 

 (mouth parts) situated between the chelipeds and 

 the mouth. Examine them on living crayfishes 

 and compare with mouth parts which have been 

 removed from dead specimens. First find the 

 mouth and then identify, — 



