too 



THE AMERICAN NATURALIST [Vol. XLIV 



ontogeny and phylogeny is obscured by the ccenogenetic 

 peculiarities of the former, so likewise the connection 

 between ontogeny and regeneration is frequently ob- 

 scured by the palingenetic peculiarities of the latter. To 

 quote: "Die Uebereinstimmung (zwischen Regeneration 

 und Embryonalentwicklung) bezieht sich gerade auf 

 palingenetische ziige, warend cenogenetische viel leichter 

 eliminiert werden" (E. Schultz). The application of the 

 principle of atavism to phenomena of regeneration has 

 been in vogue for nearly a quarter of a century, and 

 Davydoff also records what he considers cases of atavism 

 in the regeneration of Ptychodera, such as: the forma- 

 tion of two nephridial ducts instead of one ; the failure to 

 regenerate on the part of the ectodermal duct of the 

 nephridium; the regeneration of a double instead of a 

 single pericardial sac, etc. 



The novelty of Davydoff 's work consists in the at- 

 tempt to give to the principle of atavism practical 

 application. If regeneration proceeds by more primi- 

 tive methods, why not avail oneself of this opportunity 

 to throw light upon such points of animal morphology as 

 are obscured by the ccenogenetic methods of develop- 

 ment! To Davydoff belongs the full credit for having 

 ventured to accept this logical consequence of the preced- 

 ing propositions. We shall return to this question later. 

 At this moment I wish to examine the validity of the 

 so-called "atavism" theory in regeneration. 



The defects of this theory are twofold— the theory is 

 not self-consistent, and, moreover, in the majority of 

 cases it takes for granted what ought first to be proved. 

 The inducement may be strong to interpret, for instance, 

 the type of scaling on regenerating tails of lizards, totally 

 different from the normal for the given genus and yet 

 similar to that of another genus, as a "throwing back" 

 to some common ancestral condition. The appearance 

 of dorsal stripes on the regenerating tails instead of 

 usual annuli might with like justice be concei\ 

 "throwing back." But while maintaining the atavi 



