CH. XXI.] VARIOUS SPECIES OF CRABS. 285 



particular parts of the limb, and especially at the 

 joints ; and the animal seems to be aware of the 

 greater facility with which a renewal of the claw can 

 be effected at these parts ; for if it chances to re- 

 ceive an injury at the extremity of the limb, it often, 

 by a spontaneous effort, breaks off the whole limb at 

 its junction with the trunk, which is the point where 

 the growth more speedily commences. The wound 

 soon becomes covered with a delicate white mem- 

 brane, which presents, at first, a convex surface ; 

 this gradually rises to a point, and is found, on exam- 

 ination, to conceal the rudiment of a new claw. At 

 first this new claw enlarges but slowly, as if col- 

 lecting strength for the more vigorous effort of ex- 

 pansion which afterward takes place. As it grows, 

 the membrane is pushed forward, becoming thinner 

 in proportion as it is stretched, till at length it gives 

 way, and the soft claw is exposed to view. The 

 claw now enlarges rapidly, and in a few days more 

 acquires a shell as hard as that which had preceded 

 it. Usually, however, it does not attain the same 

 size, a circumstance which accounts for our fre- 

 quently meeting with lobsters and crabs which have 

 one claw much smaller than the other. In the course 

 of the subsequent castings, this disparity gradually 

 disappears. The same power of restoration is found 

 to reside in the legs, the antennae, and the jaws." 



All the species of Crustacea belonging to the great 

 division to which the lobster is referred, and which 

 have the eyes placed at the extremity of footstalks 

 (Malacostraca podophthalma), are supposed, from 

 analogy, to undergo a similar series of mountings 

 to those described above ; but it is a curious circum- 

 stance that the exuviae even of the commonest 

 species, such for instance as the crayfish (Astacus 

 fluviatilis), found in all our rivers, are very rarely 

 indeed to be met with, hence various conjectures 

 have been raised as to what becomes of them. 



The description of a remarkable parasitic animal 



