EXPERIMENTAL MORPHOGENESIS 115 



if not very improbable, that the compensation is accomplished 

 in such a purely passive way, because we know that in 

 other cases it is usually the growth of the young parts 

 that actively attracts the nourishment : there is first 

 differentiation and growth, and afterwards there is a change 

 in the direction of the nourishing fluids. 



The process of true regeneration, beginning at the 

 locality of the wound itself, has been shown by Morgan, 

 even as regards its rate, to occur quite irrespectively of the 

 animal being fed or not. 1 There could hardly be a better 

 demonstration of the fundamental fact that food assists 

 restitution, but does not " cause " it in any way. 



But in spite of all we have said, there seems to be some 

 truth in regarding the nutritive juices of animals and plants 

 as somehow connected with the stimulus of restitutions : 

 only in this very cautious form, however, may we make 

 the hypothesis. It has been shown for both animals and 

 plants, that morphogenesis of the restitutive type may be 

 called forth even if the parts, now to be " regenerated " 

 have not been actually removed ; e.g. in the so-called 

 super-regeneration of legs and tails in Amphibia, of the 

 head in Planarians, of the root-tip in plants and in some 

 other cases. Here it has always been a disturbance of the 



Compensation may occur before the function has made its appearance, as was 

 shown to be the case in the testicles and mammae of rabbits. (Arch. Entw. 

 Mech. 1, 1894, p. 69.) 



1 At any given time only the absolute size of the regenerated part is 

 greater in animals which are well fed ; the degree of differentiation is the 

 same in all. Zeleny has found that, if all five arms of a starfish are removed, 

 each one of them will regenerate more material in a given time than it 

 would have done if it alone had been removed. But these differences also 

 only relate to absolute size and not to the degree of differentiation. They 

 possibly may be due in fact to conditions of nourishment, but even here 

 other explanations seems possible (Zeleny, Journ. exp. Zool. 2, 1905). 



