ON CRUSTACEA. 
299 
Aristotle and Pliny, make mention of it ; but it has only been 
in later times that any explanation of it has been attempted. 
The time necessary to the reproduction of the new legs is 
not fixed : they grow faster in proportion as the season is 
more hot, and the animal is better nourished. Various cir- 
cumstances, again, render this reproduction more or less 
prompt : one of the most essential is the place in which the 
rupture has been made. 
If the limb of a crab or lobster has been broken during the 
summer season, and that in a day or two after the changes 
that have taken place be examined, we shall find a reddish 
sort of membrane covering the flesh. In four or five days this 
membrane assumes a convex surface, like the segment of a 
sphere ; afterwards it becomes conical, and is elongated more 
and more, in proportion as the foot which pushes it from 
underneath is developed. Finally, the membrane is torn, and 
the leg appears : it is soft at first, but in a few days becomes 
covered with a shell as hard as that of the old one. It now 
wants nothing but thickness and length, which it acquires in 
time, for with each change of skin it augments in a more rapid 
proportion than the feet which are at their full growth. 
Reaumur has attempted to explain the causes of this repro- 
duction of parts in the astaci. He inquires, if at the base of 
each leg there may not be a provision of new legs, as in chil- 
dren there is a tooth under the milk-tooth, which is one day 
destined to fall ? if a lobster can repair the loss of its limbs to 
an indefinite extent, or if after a certain number of reproduc- 
tions it be capable of no more ? with some other questions of 
the same kind. It is perfectly obvious that all these are mere 
conjectures, on which experiment throws no light, and con- 
cerning which we shall in all probability ever remain in 
obscurity. 
The antennae, antennulee, and jaws, regerminate in the same 
