Chap, v.] OF EEGENEKATION. 335 



success artificial fissifarity. The Polypus hrachiatus, the earth- 

 wonns, the naids, the planaries can be sectionised with impimity. 

 Each isolated fragment lives its own life, completes itself, and 

 becomes an entire animal. 



We can even thus create monsters. For instance, by section- 

 ising longitudinally a planary to the half of its length, Dugfes 

 was able at the end of a few days to obtain a bicephalous 

 planary. 



When an inferior animal is sectionised transversally into two 

 parts, it is the more differentiated, the more centralised the part 

 which completes itself the first. In a Polypus hrachiatus it is 

 the buccal portion which first renews itself. In the earthworm 

 the anterior fragment remakes for itself a tail before the pos- 

 terior part succeeds in refashioning a head. 



In all cases the organs of new formation are regenerated at 

 the expense of the blastemas of the portion which they complete. 

 When a snail remakes a head, when the tail of a lizard grows 

 again, when, as Spallanzani has observed, a salamander regene- 

 rates a new tail with the nerves, the muscles, the vertebrse, the 

 vessels, the skin thereof — when it creates anew claws, the lower 

 jaw, and so on, all this labour of reconstruction is achieved 

 without augmenting the weight of the trunk which has remained 

 alive. The animal has become again entire and complete, but it 

 is enfeebled, diminished. This is why it is impossible to renew 

 indefinitely the operation without causing death. The head of 

 the earthworm, for example, cannot be reproduced more than 

 twice or thrice. This is also the reason why the regenerated 

 is often smaller than the old and more imperfectly fashioned 

 part. 



By an inexplicable singularity regeneration is sometimes the 

 more certain, the larger the portion taken away is. When 

 Reaumur merely broke one or two joins of the anterior claw of a 

 crab, the loss was not repaired. On the other hand, the whole 

 claw was regenerated when it had been entirely removed.^ 

 1 K^aumur, Mimoires de I'Acadimie des Sciences, 1712. 



