CH. XII] INTERPRETATIONS AXD CONCLUSIONS 127 



general the fate of the blastomere. If the blastomeres could be 

 interchanged as can the individual marbles of a heap, then the 

 fate of each would be determined by its new position in the 

 whole. This conclusion is directly opposed to Eoux's theory 

 of a qualitative division of the blastomeres during the early 

 cleavage. 



Hertwig had also stated shortly before Driesch that in his 

 opinion the egg divides quantitatively, and that Roux's experi- 

 ments did not touch the cardinal point of this problem, because 

 the other injured half of the egg remained in contact with the 

 developing half. Hertwig expressed his belief that if the first 

 two blastomeres of the frog's egg could be separated from each 

 other, each would develop into a whole embryo. Further, he 

 thought that the development of an organism is not a mosaic 

 work, but that the parts develop in relation to one another, i.e. 

 the development of a part is dependent on the development 

 of the whole. Wilson ('93) also, from the results of a most 

 careful and important series of experiments on the egg of 

 Amphioxus, concluded that the division of the egg is not quali- 

 tative. He found that isolated blastomeres give rise to larva? 

 smaller in size than the normal, but having the normal form. 

 The differentiation of the blastomeres, Wilson thought, takes 

 place in the later periods of cleavage. 



Roux's SUBSIDIARY HYPOTHESIS 



Roux replied to the criticisms that Driesch, Hertwig, Wil- 

 son, and others have made of his theory, and attempted to show 

 that his view is fully compatible with the results that Driesch 

 and others obtained. 



Roux ('92, a, '93, b) pointed out that the results of Chabry, 1 

 Fiedler, and Chun show that in ascidians, sea-urchins, and 

 ctenophors a half-development takes place when one of the 

 first two blastomeres has been removed, and that the experi- 

 ments of Driesch also showed that an isolated blastomere 

 of the egg of Echinus cleaved as a half, and not as a whole, 

 and that a half-blastula also developed. These results indi- 



1 Later experiments have shown that this statement is not true for ascidians, 

 as Chabry's work might seem, in part, to show. 



