PHYLOGENETIC AND ONTOGENETIC PROCESSES 213 



too much neglected, and calls attention to several instances of what 

 he believes to be cases in point. He thinks that Biilow is correct in 

 his comparison between the method of development of the new tissue 

 at the end of the tail in certain naids, and the method of gastrula- 

 tion and formation of the mesoderm in the embryo. Later results 

 have shown, however, that in several points Billow's observations are 

 incorrect. The in-turning of ectoderm that Biilow compares with the 

 process of gastrulation is connected with the formation of the ecto- 

 dermal proctodaeum, and is not comparable with the development of 

 the endoderm in the embryo. 



Gotte also, as we have seen, cites a case of resemblance between 

 the regeneration of the limbs of the salamander and their mode of 

 embryonic development. He finds the resemblances less marked as 

 the animal becomes older. The resemblance is, however, not very 

 close and of a rather general sort, and since the same structures 

 develop in both cases out of the same kind of substance, it is not sur- 

 prising that there should be some resemblances in the processes. This 

 evidence is counterbalanced by the mode of regeneration of the tail 

 in the adult of certain forms, and in the regeneration of the lens of 

 the eye from the iris. 



Carriere finds that the eye of snails regenerates from the ectoderm 

 in much the same way as the young eye develops. Granted that the 

 eye is to come from the ectoderm in both cases, and that the same 

 structure develops, it is not to be wondered at that the two processes 

 have much in common. 



The mistake, I think, is not in stating that the two processes are 

 sometimes similar, or even identical, but in stating the matter as 

 though the regenerative process repeats the embryonic method of 

 development. If the same conditions prevail, then the same factors 

 that bring about the embryonic development may be active in bring- 

 ing about the regenerative processes. In fact, we should expect 

 them to coincide oftener than appears to be the case, but this may 

 be due to the conditions being different in the young and in the 

 adult. 



It has been claimed also that in some cases there is regenerated a 

 structure like that possessed by the ancestors of the animal. The 

 stock example of this process is Fritz Miiller's result on the regener- 

 ation of the claw of a shrimp, Atypoida protiminim^ Fraisse and 

 Weismann and others have brought forward this case as demonstra- 

 tive. The animal is said to regenerate a claw different from any of 

 those in the typical form, and one that resembles the claw of another 

 related genus, Carodina. The value of evidence of this sort is not 

 above question. Przibram has shown in other Crustacea that when 



1 Cosmos, Vol. VII, p. 388. 



