CHAPTER FOUR 



PHENOMENA WHICH REFUTE SIMPLE EPIGENESIS ; AND 

 PHENOMENA WHICH REFUTE PREFORMATION. INAD- 

 MISSABILITY OF A HOMOGENEOUS GERM SUBSTANCE; 

 AND INADMISSABILITY OF PREFORMISTIC GERMS. 



I. Phenomena Which Refute Simple Epigenesis 



Roux designates, with the expression "self-differenti- 

 ation" of a certain part of the organism, the process in 

 which, according to a certain hypothesis, "the cause of 

 whatever is specific in the differentiation of that part lies 

 within this latter." And he calls "dependent or correla- 

 tive differentiation" the opposite process, in which, ac- 

 cording to other hypotheses, whatever is specific in the 

 alteration which goes on in a certain part of the organism 

 during development is determined by causes lying outside 

 this part. 69 



If an ontogeny consisted only of self-differentiations, 

 we should designate the development as evolutionary. If 

 on the contrary, an ontogeny were produced only through 

 dependent differentiations, we should call that a process 

 of epigenetic nature. 



"Wilhelm Roux: Die Methoden zur Hervorbringung balber 

 Froschembryonen und zum Nachweis der Beziehung der erstcn 

 Furchungsebene des Froscheies zur Medianebene des Embryo. Anat. 

 Anzeiger, Bd. IX. February 1894, P. 277 278. Gesamm. Abhandl., 

 II, P. 978. 



104 



