264 THE MECHANICAL FUNCTIONS. 



Reaumur, that this new growth takes place more 

 readily at particular parts of the limb, and espe- 

 cially at the joints ; and the animal seems to be 

 aware of the greater facility with which a renewal 

 of the claw can be effected at these parts ; for if it 

 chance to receive an injury at the extremity 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 com- 

 mences. The wound soon becomes covered with a 

 delicate white membrane, which presents at first a 

 convex surface : this gradually rises to a point, and 

 is found on examination to conceal the rudiment of 

 a new claw. At first this new claw enlarges but 

 slowly, as if collecting strength for the more vigo- 

 rous efltbrt of expansion which afterwards takes 

 place. As it grows, the membrane is pushed for- 

 wards, becoming thinner in proportion as it is 

 stretched ; till at length it gives way, 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 cir- 

 cumstance which accounts for our frequently meet- 

 ing with lobsters and crabs which have one claw 

 much smaller than the other. In the course of the 

 subsequent castings, this disparity gradually dis- 

 appears. A similar power of restoration is found 

 to reside in the legs, the antennae, and the jaws. 



We must naturally be curious to learn, if pos- 

 sible, from what source these astonishing powers 

 of regeneration are derived. Reaumur hazarded 

 the conjecture, that there might be originally im- 

 planted in each articulation a certain number of 



