1899] REGENERATION 317 



legs of insects must have been capable of regeneration from the first, 

 but may have entirely or partially lost this power in many groups, 

 or have so modified it that it remained only at certain definite regions, 

 as in the Phasmidae. Were the power of regeneration once lost it is 

 scarcely possible that it should ever have been regained. 



Autotomy, on the other hand, is an adaptation which might, phylo- 

 genetically speaking, arise anew at any time, where necessary, assuming 

 that the existing parts were capable of varying and adapting themselves 

 to that end. The existence of an autotomic adaptation of an analogous 

 though not quite identical kind in insects and in crabs shows that the 

 adaptation could take place in both classes, and the presence of such 

 an adaptation in relation to the three anterior thoracic legs of Pagurus, 

 together with its absence in relation to the fourth and fifth legs 

 (Morgan), is further evidence of the comparatively recent introduction 

 of autotomy and the much older origin of regeneration ; for the fourth 

 and fifth pairs of legs possess the power of regeneration. 



The adaptation for autotomy once gained, the power of regenera- 

 tion had of necessity to become localised ; that is to say, the apparatus 

 necessary for it had to be transferred to those parts at which alone the 

 breaking off of the limb occurs in response to certain definite stimuli. 

 In any case, however, both capacities are " Mnrichtungen," that is, 

 adaptations of the organism to definite demands made ttpon it by the 

 conditions of life, and are not the outcome of primary qualities of the 

 living substance. In regard to autotomy this is immediately clear 

 because we know the reflex mechanism and the modification of the 

 breaking-point upon which the adaptation depends, but in the case of 

 regeneration we can in the meantime only guess at the mechanism 

 which brings it about. That there is some special mechanism hardly 

 admits of dispute. 



In the beginning of the paper from which I have quoted above, 

 Morgan casts a glance at my theory of regeneration as an adaptation- 

 phenomenon, and not exactly a friendly glance either ; for it seems to 

 be the fashion nowadays among the younger investigators to look 

 down with a certain lofty disdain upon so-called " explanations " which 

 are based upon the selection-hypothesis. Morgan cannot believe that 

 the chapter on regeneration in the-" Germ-Plasm" will convince any one 

 that the phenomena are " in any way " there explained, and he reaches 

 a climax in the dictum, " it seems that the ' Natur-philosophie ' is not 

 yet dead." To that I can only answer : It is to be hoped that it is 

 not, and that it never will be dead, for progress in our knowledge 

 will always depend upon the philosophical treatment of known facts, 

 since it is only in this way that we can set up new goals to guide our 

 observations, and so find out new facts which will give us a deeper 

 insight, — only in this way, too, can we recognise the importance of the 

 facts which chance reveals to us. But if Morgan means by " Natur- 

 philosophie " merely the degenerate varieties of philosophical Nature- 



