REGENERA TION. 1 9 1 



piece. The same thing is true for the earthworm, in which, if 

 the piece be cut off behind the fifteenth segment, no new 

 reproductive region is ever developed. Pfltiger's view leaves 

 the absence of this region unaccounted for. 



Weismann, in his book on the Germ Plasm published in 

 1893, elaborated an hypothesis of regeneration. Weismann's 

 central idea is not different from Bonnet's (1768). Both be- 

 lieve in preformed germs. The differences in their views 

 result largely from the application of modern cell doctrines 

 to Weismann's hypothesis. Regeneration is supposed to be 

 brought about by latent cells containing preformed germs 

 which exist in the chromosomes of the nucleus in the form of 

 determinants. There are supposed to be cells of this sort in 

 the leg of a newt, for instance, at every level and in all the 

 parts. At each level the latent cells are slightly different, and 

 each contains germs of such a sort that all the distal part and 

 only the distal part is represented. This germ stuff, coming 

 into action after a series of qualitative nuclear divisions, influ- 

 ences the part in which it is found. Further, since the new 

 limb will itself regenerate if cut off, the further assumption is 

 made that during regeneration new subsidiary germs are laid 

 down at each level in the new limb. This is supposed to take 

 place by a division of each germ into like parts (a quantita- 

 tive division) after it has reached its proper position in the 

 new leg. 



This host of invisible germs, moving at the command of 

 Weismann's imagination, is supposed to carry out the process 

 of regeneration. No one can fail to see that the difficulty is 

 only shifted into a region where fancy can have free play and 

 a scientific, experimental test cannot be applied. At one blow 

 the difficulties are overcome, and the array of mystical germs 

 is summoned to explain how regeneration takes place. 



Since regeneration occurs in some animals and not in others, 

 and better in those forms, Weismann thinks, that are liable to 

 injury, additional hypotheses are added. Weismann combats 

 the idea that regeneration is the result of the inherited effect 

 of injuries to the part. The Lamarckian conception cannot 

 apply in this case, since it is not the use or disuse of a part 



