The Recapitulation Theory in Biology 47 



The question thus becomes one of accurate description, of 

 the greatest difficulty necessarily, in view of the peculiar nature 

 of the facts upon which all inferences as to ontogenetic-ancestral 

 comparisons rest. In the following extract from Minot is pre- 

 sented an illustration of a somewhat closer approach to the 

 comparison than is customary: 



"One of the first things which will impress itself upon the 

 student of vertebrate embryology is, that, though he may find 

 at the proper stage in the embryo the organs of the body clearly 

 developed, yet, owing to the fact that they consist of relatively 

 undifferentiated cells, they are incapable in large part, of per- 

 forming functions which they are ultimately to assume, and the 

 performance of which is the very object of their development. 

 This change in histological structure brings about a marked 

 unlikeness of the embryo to the assumed ancestral type." 77 



The main point of difference between Montgomery and Cum- 

 ings, is, however, not one of logical form merely, but turns upon 

 a significant question of fact. This has to do with the manner 

 in which the specific differences, which by general consent reside 

 n the germ-cell, affect the subsequent course of development. 

 Do these differences express themselves equally upon all periods 

 of ontogeny, and so disturb "the whole row' 7 of stages, as 

 Montgomery implies, or can they be regarded as relatively 

 unimportant in certain phases and highly important in others, 

 as suggested by Cumings? Does a variation affect the entire 

 ontogeny uniformly, or does it exhibit itself at a given period 

 when the conditions are favorable? In short, how much liberty 

 has any phase of growth to evolve by itself without markedly 

 disturbing other phases? 



The facts, as reported by the investigators, seem to favor the 

 suggestion of Cumings. Thus in the language of Driesch, 



"... .the actual fate of a part need not be identical with its 

 possible fate, at least in many cases ; . . . . There are more morpho- 

 genetic possibilities contained in each embryonic part than are 

 actually realized in a special morphogenetic case." 78 



That is to say, the fate of a part is determined in some degree 

 in the course of its subsequent history. A complementary 

 thought is embodied in these words of Morgan: 



77 Laboratory Text Book in Embryology, 2d ed., 1910, p. 14. 



The Science and Philosophy of the Organism, Vol. 1, 1909, p. 77. 



