EPIGENESIS OR EVOLUTION. 121 



E. B. Wilson in the article which I have already quoted, in 

 which he seeks to reconcile the hypotheses of Weismann and 

 Roux with the observations made by Driesch and himself 

 on the cleavage of isolated blastomeres. Wilson's attempts 

 to reconcile these apparently conflicting views are attractive, 

 since they include a reconciliation of an evolutionary with 

 an epigenetic theory of development, as is evident from his 

 own words : " The entire series of events is primarily deter- 

 mined by the organisation of the undivided ovum that 

 forms its first term, and, as such, conditions every succeed- 

 ing term. The morphological value of the individual blasto- 

 mere at any particular stage is the product of two factors, 

 one of which (the embryonic environment) is external, while 

 the other (the nature of the idioplasm) is internal." 1 



A curious confusion, as it seems to me, has been intro- 

 duced into these discussions by the use of the term, " mosaic 

 work," invented by Roux to signify "a whole formed out 

 of several or many self-determining parts ". Now there is 

 nobody who has seen a mosaic, and knows how it was made, 

 who would describe it as beingf formed out of self-determining- 

 parts. With all respect to the judgment of Roux, I have 

 always thought of a mosaic as formed out of parts whose 

 position was determined by forces lying altogether outside 

 themselves, namely, by the artist who designed the mosaic, 

 and the workmen who put the parts together, and this, I 

 take it, would be the opinion of every sensible man. The 

 name mosaic can only be properly applied to a whole, 

 the parts of which owe their position to an external con- 

 trolling force : it is not in the least applicable to a whole, 

 the parts of which are self-determining. In point of fact, 

 the name mosaic is applicable to epigenesis, not to evolution, 

 and was so applied by Huxley long ago. 2 If I understand 



1 Op. cit., p. 614. 



2 " For Schwann, the organism is a bee-hive, its actions and forces 

 resulting from the separate but harmonious interaction of all its parts. For 

 Wolff, it is a mosaic, every portion of which expresses only the conditions 

 under which the formative power acted, and the tendencies by which it 

 was guided" (The " Cell Theory," Medico- Chirurgical Review, xii., 1853, 

 P- 295)- 



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