H2 Phenomena Refuting Simple Epigenesis 



But the preformationists on their side cite certain partic- 

 ular cases of regeneration as unfavorable to epigenesis: 

 "Regeneration" remarks Roux, "takes place in tritons 

 when all four extremities are removed at one time, from 

 which it follows that for the formation of new extremities 

 in one antimere, the presence of the other extremities 

 is not in the least necessary, so that for this formation 

 it is not necessary that there be any formative correlating 

 influence extended from them." 74 



The anachronisms of development in which, for 

 instance, certain parts remain behind other parts in their 

 formation, or in which the germ layers may even develop 

 with uneven speed, or one entire half of the body may 

 take a jump ahead of the other half so that one can 

 sometimes observe two different degrees of development 

 in the two halves of the same embryo, belong likewise 

 to the number of phenomena which simple epigenesis is 

 incapable of explaining: "How the (epigenetic) con- 

 ceptions of O. Hertwig," Roux writes further, and his 

 words, already quoted above, deserve to be repeated here, 

 "can be reconciled with these anachronisms in the 

 development of the germ layers which I have observed, 

 or indeed with the absence of the lower layer the endo- 

 blast (Anentoblastia), while both of the other two layers 

 remain essentially normal in the disposition of their 

 parts, or finally with the formation of half embryos, may 

 well be left to the reader's own judgment. For if such 

 large parts can remain behind in their development, or 

 indeed be lacking altogether, and the other parts be in 

 no wise disturbed thereby in their development, it surely 

 follows that the development of these latter is not con- 



74 Wilhelm Roux : Uber Mosaikarbeit etc. Anat. Hefte, Febr. 

 1893, P. 299. Gesamm. Abhand. II, P. 839. 



