No. 518] 



BEGENERATION 



not concern myself with this side of the matter, as it is 

 my prime object in the present article to scrutinize Davy- 

 doff ? s theoretical position. 



On the very first pages Davydoff* states the main 

 article of his creed: that the fact that new organs, in the 

 process of regeneration, originate from the same layers 

 from which such organs originated embryological Im- 

 proves that the two processes are parallel in cause. 

 Since the hypothesis of the repetition of the phylo- 

 genetic processes in regeneration necessarily rests upon 

 this assumption, as a major premise, it may be well, in 

 the first instance, to examine closely its validity. This 

 plan is preferable also because Davydoff himself in im- 

 parting his data and defending his thesis follows a sim- 

 ilar course. 



The reader is doubtless familiar with the way a com- 

 parison of the two-layered gastrula with an adult Coe- 

 lenterate had ultimately grown into Haeckel's celebrated 

 * ' Gastraea-theorie. " This broad embryological concep- 

 tion, purporting to bind the entire animal kingdom with 

 bonds of genetic relationship, postulates the homology of 

 adult organs differentiated from similar germ-layers in 

 the embryos. So fascinating was the application of this 

 greatest biological generalization that the overweening 

 confidence it bade became in time a source of grievous 

 blunders. Contradictions have arisen on the ground of 

 striking differences in the origin of organs in develop- 

 ment and in budding, as was discovered to be the case 

 in Bryozoa and in Tunicates. Likewise the discrepancy 

 often observed between the methods of organ-formation 

 in ontogeny and regeneration tended further to under- 

 mine credulity in the theory and the value of the germ- 

 layers as a criterion of homology. Indeed, so seriously 

 was this aspect of the theory threatened that conserva- 

 tive men, like L. Schultze, anxious to safeguard it from 

 impending disrepute, were obliged to eliminate instances 

 of budding and of regeneration from a consideration of 



