22 REGENERATION 



the factors that are present in the two cases appear to be in large part 

 the same, and while it may be convenient to put into one class those 

 cases in which proliferation precedes the formation of the new organs, 

 and into another class those cases in which the change takes place 

 without proliferation, yet, since the distinction is one of subordinate 

 value, it is necessary to have one word to include both groups of 

 cases ; and no better word than regeneration has, I think, been as yet 

 suggested. 



Driesch has made use of two other descriptive terms. The word 

 " reparation " is used to describe the development of the hydranth of 

 tubularia. The new hydranth is formed in this case out of the old 

 tissue at the end of the piece (Fig. 20, A). The change appears to be 

 the same as that which takes place in a piece of hydra, etc. The word 

 "reparation" does not seem to me to express very satisfactorily this 

 sort of change, or sharply separate it from those cases in which the 

 animal is repaired by adding what has been taken away ; but in this 

 latter sense Driesch does not use the term. I have not made use of 

 the word, in general, except as applied to Driesch's work. 



Another term, "regulation," used by Roux^and also by Driesch and 

 others, is used in a sort of physiological sense to express the readjust- 

 ments that take place, by means of which the typical form is 

 realized or maintained. By inference we may extend the use of the 

 word to include the changes that take place in the new material, that 

 is proliferated in forms that regenerate by this method. Driesch 

 uses this term, regulation, to include a much more general class of 

 phenomena than those included in the term regeneration, as for in- 

 stance, the regulation of metabolism and of adaptation, etc. One of 

 the subdivisions of the term regulation is called "restitution." This 

 word also is used where I should prefer to use the word regeneration as 

 a general term, and the word reorganization when reference is made 

 to the internal changes that lead to the production of a typical 

 form. 



Both Roux and Driesch also speak of " self-regulation," by which is 

 meant, I suppose, that the changes taking place are due to readjust- 

 ments in the part itself, and are not induced by outside factors. The 

 expression " self-regulation " is not, I think, a very happy one, since 

 all change is ultimately dependent upon a relation between inside and 

 outside conditions. 



Hertwig 2 defines regeneration as the power of replacement of a 

 part of the organism. He states that in all cases the beginning of 

 the process is the same, viz. the appearance of a small protuberance 

 composed of cells, that is the rudiment of the new part. It is evident 



1 As used in connection with other terms, see his Ges. Abhandl., Vol. II, page 41. 



2 Die Zelle und die Gewebe. 



