2Q RE GENERA TION 



eration has been for a long time in general use to include all such phe- 

 nomena as those referred to, but amongst recent writers there is some 

 diversity of opinion as to how much is to be included in the term, and 

 the question has arisen as to the advantage of applying new names 

 to the different kinds of regeneration. There can be little doubt of 

 the advantage, for the sake of greater clearness, of the use of different 

 terms to designate different phenomena, but I think that there is at 

 the same time the need of some general term to cover the whole field, 

 and the word regeneration, that is already in general use, seems to 

 fulfil this purpose better than any other. 



Roux l points out that Trembley, and later Nussbaum, showed 

 that a piece of hydra regenerates without the formation of new mate- 

 rial. Roux adds that since during development the piece takes no 

 nourishment, the regeneration must be brought about by the rearrange- 

 ment of the cells present in the piece. 2 The change may, or may 

 not, involve an increase in the number of the cells through a process 

 of division. In consequence of this method of development a re-dif- 

 ferentiation of the cells that have been already differentiated takes 

 place. This process of regeneration, Roux points out, is very similar 

 to the " post-generation " of the piece of the blastula of the sea-urchin 

 embryo, and he concludes that " regeneration may be brought about 

 entirely, or very largely, through the rearrangement and re-differen- 

 tiation of cells without any, or with very little, proliferation taking 

 place." In the adults of higher animals regeneration by prolifera- 

 tion preponderates, but rearrangement and re-differentiation of cells 

 occur in all processes of regeneration, even in higher vertebrates. 

 The two kinds of regeneration that Roux distinguishes are, he says, 

 essentially quantitative. 3 



1 Gesammelte Abhandlungen, No. 27, p. 836. 



2 The fact that the piece does, or does not, take in food has no bearing on the question, 

 since many animals that do not feed while the regeneration is going on produce new cells to 

 form the new part. 



3 These two kinds of regeneration are post-generation and regeneration proper. The 

 distinction that Roux attempts to make between these two processes is to a certain extent 

 artificial and rests at present on a very unsafe basis, at least in so far as the post-generation 

 of the frog's embryo is taken as a representative case of this process. Roux states that in 

 the process of regeneration the injured tissues produce each their like in the new part, while 

 in the process of post-generation of the frog's egg the new cell-material arises in part from 

 the nuclei and yolk-material of the injured half and in part through the accidental posi- 

 tion of the nuclear material of the uninjured half. In order more fully to understand this 

 distinction the original description of the process of post-generation given by Roux in his 

 account of the development of half embryos of the frog's egg must be referred to. In later 

 papers Roux pointed out that the missing half of the frog embryo, as well as of other forms, 

 may be post-generated without any new material appearing at the open side of the embryo. 

 It is unfortunate, I think, that the original term should have been extended to include these 

 other processes that do not partake of the nature of post-generation as at first denned, but 

 are more like the true process of regeneration as described by Roux. 



