CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 126 



into segments similar to the body of an eartiiworni. Tlie 

 ceplialotliorax is also segmented; but the segmentation is 

 obscured on the dor- 

 sal surface by the 

 carapace, but sho^vs 

 plainly on the ventral 

 side. 



The appendages of 

 the abdomen. — Each 

 segment of the abdo- 

 men (in the male), 

 except the last, beai's 

 a pair of appendages 

 known as the sivwi- 

 merets. These are 

 small, segmented, leg- 

 like organs held close 

 under the abdomen, 

 with the exception of 

 the last pair. These 

 are broad and flat, 

 and, together with 



Fig. 6S.— Crayfish. 



the last segment of the abdomen , the ielson, form the tail 

 fin, or swimming fin. In the female, the first two pairs of 

 swimmerets are either very small or altogether lacking. 



Appendages of the cephalothorax. — The appendages of 

 the cephalothorax may be divided into five groups: the 

 walking legs, five pairs; the foot jaws, or 7naxil]tpeds, three 

 pairs; tlie jaws, two pairs of maxilla? and one pair of man- 

 dibles; the antenna?, or feelers, one pair; and the antemiules, 

 one pair. 



The walking legs ai'O attached to the thorax and each 



