210 THE MECHANICAL FUNCTIONS. 



time replaced by a new claw, which grows from the stump 

 of the one which had been lost. It appears from the inves- 

 tigations of Reaumur, that this new growth takes place more 

 readily at particular parts of the limb, and especially at the 

 joints; and the animal seems to be aware of the greater fa- 

 cility with which a renewal of the claw can be effected at 

 these parts; for if it chance to receive an injury at the ex- 

 tremity 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 gradu- 

 allv rises to a point, and is found on examination to conceal 

 the rudiment of a new claw. At first this new claw en- 

 larges but slowly, as if collecting strength for the more vigo- 

 rous effort of expansion which afterwards takes place. As it 

 o-rows, the membrane is pushed forwards, becoming thin- 

 ner in proportion as it is stretched; till at length it gives 

 wMy, 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 frequently meeting with lobsters and crabs wdiich 

 have one claw much smaller than the other. In the course 

 of the subsequent castings, this disparity gradually disap- 

 pears. The same power of restoration is found to reside in 

 the legs, the antennse, and the jaws. 



We must naturally be curious to learn, if possible, from 

 what source these astonishing powers of regeneration are de- 

 rived. Reaumur hazarded the conjecture, that there might be 

 orio^inally implanted in each articulation a certain number of 

 embryo limbs, ready to be developed as occasion might re- 

 quire; somewhat in the way in which the rudiments of the 

 secondary teeth remain concealed in the jaw, in preparation 

 for replacing the first set when these have been removed. 

 But this hypothesis is overturned by the fact that if the ani- 

 mal loses only part of the limb, it is the deficient portion 

 alone, and not the whole limb that is regenerated. The 



