GENERAL INTRODUCTION 2$ 



that Hertwig has taken into account only one side of the process. 

 Those cases in which a rearrangement or reorganization takes place 

 in the old part are not even considered. 1 Goebel 2 points out that in 

 plants the fully formed cells are, as a rule, incapable of further growth 

 after they have once served as a basis of an organ of the body, but 

 often some of the cells may remain in a latent condition, and grow 

 again, when the intercellular interactions are disturbed. This is the 

 case, he thinks, in regeneration. Goebel speaks of regeneration by 

 means of adventitious buds in those cases in which the buds had not 

 previously existed before the removal of the part. In those cases in 

 which the buds are in existence before the piece is removed, as in 

 the leaves of Asplenium, Begonia, etc., the development is not the 

 result of regeneration, Goebel thinks, but the buds represent a stage 

 in the development of the species. It may be pointed out, however, 

 that it is certainly a remarkable fact that often the conditions that 

 lead to the unfolding of an existing bud are the same as those that 

 lead to the development of a new bud. 



The preceding account will suffice to illustrate some of the princi- 

 pal ideas that are held in regard to the process of regeneration. 

 Since many new facts have come to light in the last few years, it may 

 not be amiss to point out what terms will be used in the following 

 pages to include each kind of process. 



The word " regeneration " has come to mean, in general usage, not 

 only the replacement of a lost part, but also the development of a 

 new, whole organism, or even a part of an organism, from a piece of 

 an adult, or of an embryo, or of an egg. We must include also those 

 cases in which the part replaced is less than the part removed, or even 

 different in kind. 



At present there are known two general ways in which regenera- 

 tion may take place, although the two processes are not sharply 

 separated, and may even appear combined in the same form. In 

 order to distinguish broadly these two modes I propose to call those 

 cases of regeneration in which a proliferation of material precedes the 

 development of the new part, "epimorphosis." The other mode, in 

 which a part is transformed directly into a new organism, or part 

 of an organism without proliferation at the cut-surfaces, " morphal- 

 laxis." 



In regard to the form of the new part, certain terms may be used 

 that will enable us to characterize briefly different classes. When the 

 new part is like that removed, or like a part of that removed, as when 

 a leg or a tail is regenerated in a newt, the process is one of " homo- 



1 Hertwig's description of the method by which a piece of hydra makes a new one shows 

 that he did not understand the kind of change that takes place in this animal. 



2 Organographie der Pflanzen, '98. 



