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 ii 

 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 tive 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 antenuEe, antennuloe, and jaws, regerminate in the same 



