CRAB. 
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490 
cated; others perfectly smooth: some are furnish- 
ed with very strong and large chelm or claws ; 
others have only .weak, unarmed feet: lastly, some 
are remarkable for their great size, while others 
are so diminutive as to require the assistance of 
glasses in order to determine the structure of their 
several parts. 
The animals of this genus cast their shells from 
time to time. When tliis period approaches, the 
limbs gradually shrink or waste in size, so as to 
enable them to be drawn with greater ease from 
the claws and other parts of the shell. The animal 
then lies in a quiet state for some days, till the 
new shell is formed, or rather till it is hardened; 
for at first it is rather membranaceous than crusta- 
ceous. Some species have the body naturally desti- 
tute of a shelly covering; in consequence of which 
they never fail to take possession of such vacant 
univalve shells as happen to suit their conveni- 
ence; the body being immersed in the shell, while 
the claws remain exserted. 
The loss of a limb, an accident so dreadful and 
irremediable to the ma,jor part of the animal world, 
is to these creatures of but little importance; since 
the space of a few weeks supplies the defect, and 
restores them to their former state. Wliat is still 
more wonderful, these animals, Avhen injured, 
maimed, or bruised on any jiarticular limb, do 
not wait for the process of a gradual recovery of 
that individual })art, but, as if conscious of the 
power of reproduction, voluntary cast off with 
sudden violence the offending member, and bc- 
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