No. 518] 



REGENERATION 



97 



variations within the widest limits, it may be possible to delineate the 

 normal course or type of regeneration (p. 1G). 



Without any intention on my part to detract from 

 Davydoff's merits of having- accurately ascertained the 

 facts of the regeneration of Enteropneusta, it neverthe- 

 less seems to me that the manner of his argument is more 

 entertaining than convincing. 



Here, for instance, are samples of his reasoning. In 

 Ptychodera (Enteropneusta) the new coelome regener- 

 ates from elements of the old coelome, i. e., the new 

 mesoderm arises from old mesoderm. So far, so good. 

 DavydorY, however, is not fully satisfied with this achieve- 

 ment, as he is determined to prove to his reader that the 

 parallelism between ontogeny and regeneration is of a 

 far more subtle nature; but he encounters a stumbling 

 block in that the coelome in ontogeny arises as an evagi- 

 nation of the primitive endoderm. In the regeneration 

 of the coelome, however, the endoderm takes no direct 

 part. Is that to be regarded as a discrepancy between 

 ontogeny and regeneration? Sensible men might say 

 that since the old coelome had been differentiated from 

 endoderm, therefore, the new co j lome regenerating from 

 the old coelome is likewise of endodermal origin, and 

 would let the matter rest there. Davydoff is not con- 

 tented with this sort of proof. He finds that in Balano- 

 glossus koivaleivskii the coelome of the collar arises not 

 as an independent outgrowth from the primitive gut, but 

 is formed by proliferation of cells from the coelomic 

 pouches of the body. In other words, in Balanoglossus 

 koivaleivskii the coelome of the collar originates not 

 directly from the endoderm, but indirectly from the al- 

 ready differentiated coelome of the body. Is not this a 

 wonderful identity between the processes of regenera- 

 tion and ontogeny in Ptychodera and Balanoglossus? 



But how is it with the coelome of the proboscis? In 

 Ptychodera it regenerates by proliferation of cells from 

 the coelome of the collar. Does it arise in the same man- 

 ner in the course of ontogeny \ Davydoff appears a little 



