I70 Regeneration 



piece. (This is true, however, only in rather small 

 pieces.) There is, therefore, in small pieces a rough pro- 

 portionality between size of head and size of regenerat- 

 ing piece. Driesch' uses this interesting fact to prove 

 the existence of an entelechy, while we are inclined to 

 see in it an analogue to the observation of Leo Loeb, 

 that the velocity of the process of healing in the case 

 of a deficiency of the epithelium decreases when the 

 size of the uncovered area diminishes. While we do 

 not wish to offer any suggestion concerning the me- 

 chanism of these quantitative phenomena — they may 

 be related in some way with the velocity of certain 

 chemical reactions — we see no reason for assuming 

 that they cannot be explained on a purely physico- 

 chemical basis. 



The writer noticed that certain pigmented cells 

 from the entoderm of the organism always gather at 

 that end where a new polyp is about to be formed. 

 These red or yellowish cells always collect first at the 

 oral end of a piece of stem. It may be that certain 

 substances given off by the pigmented cells at the cut 

 end are responsible for the polyp formation, but this is 

 only a surmise. 



Another suggestion made by Child, ^ is that there 

 exists an axial gradient in the stem whereby the cells 



^ Driesch, H., Science and Philosophy of the Organism, i., 127, 

 'Child, C. A'l., "Die physiologische Isolation von Teilen des Organ- 

 ismus," Roux's Vortrdge und Anfsdtzey Leipzig, 191 1. 



