Crustacea. 7549 



very plumose character ; a somewhat analogous example may be 

 found on our own shores in the genus Calissoma, among the Amphi- 

 pods, where the terminal nail or point is broken up into fine hairs. 



The habits of those Crustacea which have feathered chelte are not 

 known, but the common soldier crab of our shores has the posterior 

 pair of feet, though not developed into a plumose brush, yet so plen- 

 tifully covered with hairs as to become an efficient brush ; with 

 this brush the animal cleans and mops out the branchial chamber and 

 the many joints and crevices of his body ; stopping now and again to 

 wipe this brush in the Gnathopoda with the greatest care. This little 

 brush is also formed as a claw, with which he pulls off any extraneous 

 matter that the softer brush cannot remove. I never thought of it 

 before, perhaps he scratches himself with it also. I wonder if a crab 

 ever felt the sensation of tickling ? Upon the softer portion of the body 

 the soldier crab is very sensitive, and always keeps it enclosed within 

 a shell of a mollusk, to preclude it from rough accidents. The way 

 that I generally get them to come out of these shells, without rough- 

 handling, is by pricking them through a hole in the apex of the shell 

 in which they dwell. Then to see their look of surprise as they hurry 

 out ! but I must not forestall. The claws of the crab and lobster are 

 not the same as those developed as such in the Amphipods and other 

 Crustacea. 



I should premise that a Crustacean is divided into three parts — 

 the head (cephalon), the body (pereion), and the tail (pleon). To 

 the pereion there are always seven pairs of limbs. In the higher 

 forms the two first are developed as to belong to the mouth, and, 

 therefore, in the crab and lobster we find the third pair in position 

 become the hands, whereas in Squilla and in the Amphipods they 

 are formed of those which are only appendages to the mouth in the 

 crab ; thus there appears a uniform' law in Crustacea that the lower 

 the type the more limbs are developed upon the simple form of the 

 true leg, — a law that is consistent with the internal structure, since 

 we find the nervous system more distinctly marked by separate 

 ganglea. 



I stated a short time back that, in order to relieve itself, a crab will 

 run away and leave one of his limbs behind. This is a piece 

 of economy in the habits of the animal common to most Articulata, as 

 well as others even of a higher order ; the legs of young frogs will, 

 upon being removed, be again reproduced ; but nowhere is the power 

 so forcibly exemplified as in the Crustacea. 



I kept some crabs for some time in order to exi)erimcnt upon these 



