THE WONDER OF LIFE 553 



cules contended, for he found to his delight that it could be 

 multiplied by being cut in pieces. It was then that Spal- 

 lanzani showed that the earthworm cut by the spade might 

 re-grow a new tail or even a new head. Bonnet made 

 numerous experiments on other worms and thought out an 

 elaborate theory. Reaumur, with his wonted insight, 

 advanced to an almost modern position when he pointed 

 out the advantage of the regenerative capacity in animals 

 which were in the natural conditions of their life exposed 

 to frequent risk of breakage or wounds. 



Instances of Regeneration. During the last twenty 

 years there has been a boom of experimental work bearing 

 on regeneration chiefly for the~reason that the pheno- 

 mena throw light on the physiology of development. Many 

 remarkable facts have come to light, of which the following 

 are typical : half of the highly differentiated Infusorian 

 Stentor can quickly regenerate the missing half and minute 

 slices across the cell can re-grow the whole ; from one 

 Planarian worm six or more may be produced by cutting 

 it into pieces ; a starfish can re-grow a lost arm, and the 

 lost arm can complete a new starfish ; a crab can re-grow a 

 lost limb ; if the eye-bearing horn of a snail be cut off, it is 

 regenerated over and over again, with the complex eye 

 complete ; if the front of the eye of a newt be cut off, a 

 new lens is regenerated ; a lizard can re-grow the tail 

 which it has surrendered to its enemy ; and a stork can 

 re-grow a considerable portion of its lower jaw. 



There is in certain types a remarkable exuberance of 

 regenerative power. This is notably true of Amphibians. 

 If the fore-limb of a newt or salamander is cut off across 

 the humerus, it is normally re-grown, and this happens 

 whether it is an adult or a larva. Nay more, in the same 



