Ihe Crayfish and the Crab. 71 



It is nearly all head-thorax. The abdomen is very- 

 small, and is tucked up under the thorax. The carapace 

 is broader than it is long. The eyes are nearly hidden 

 in two hollovrs under the edge of the carapace. The car- 

 apace has no beak, and the antennae are very small. The 

 great claws are bent like two arms, so that the crab can 

 bring them up to his mouth. All the small walking-legs 

 end in points. The mouth-parts are covered by two 

 plates. 



These two platea are really the enlarged joints of the third pair 

 of jaw-feet. 



Turning back the abdomen, we find nothing that can 

 be called a swimmeret, but either two or four pairs of ap- 

 pendages, used by the female in carrying the eggs. The 

 abdomen, no longer used in swimming, has become as 

 small as possible, and is safely kept out of the way- 



But the crab is like the lobster in some respects. It 

 has head-thorax and abdomen. Its skeleton is a hard 

 shell. It has five pairs of legs, and one pair has great 

 claws. It has some mouth-parts. It has two pairs of 

 antennae. It has eyes on stalks. 



By removing the nnder side of the carapace, which covers the 

 gills, and the third pair of jaw-feet, which hide the other month- 

 parts, we complete the proof that the namber of appendages on the 

 head-thorax and the whole plan of structure are identical with 

 what we are so familiar with in the lobster. 



