218 THE DIFFERENT SEGMENTS. 



The somites, or segments, may be described as follows, 

 beginning at the animal's posterior extremity : 



The last segment is called the " telson," and is with- 

 out appendages. It forms the final articulation of the 

 abdomen. 



To the next segment, or last but one, is attached a 

 pair of natatory appendages, the " swirnmerets," each con- 

 sisting of a basal joint which articulates with the ster- 

 num, and is called the " protopodite ; " and of two diverg- 

 ing joints, the "exopodite" (which is the outer), and 

 " endopodite" (which is the inner), attached to the for- 

 mer. These joints are considerably expanded, so as to 

 form powerful paddles ; and the outer one, or exopodite, 

 is divided by a transversal joint. 



The third segment carries a pair of "swimmerets" 

 resembling those already described, except that they are 

 much narrower, and that the exopodite is not divided. 



In the succeeding segment the extremities of the limbs, 

 or ambulatory appendages, are not simply pointed, but 

 converted into nipping claws, or " chelae." 



The next segment carries a pair of chelate limbs, 

 exactly like the preceding ; and the next, or sixth, is fur- 

 nished with appendages essentially similar in structure, 

 but much larger, and constituting the "great claws." 



The next two segments of the thorax, and the one in 

 front of them, are provided each with a pair of modified 

 limbs, which are termed " maxillipedes," or " foot-jaws." 

 These are so modified as to serve as instruments of mas- 

 tication. 



The next two somites, or segments, carry appendages in 

 the form of jaws, and are termed respectively the first 

 and second pairs of " maxillae." Each consists, as before, 



