Organisms from Eggs 139 



the main mass of the intestine-forming material ; where 

 the main mass of this body is located the invagination 

 of the intestine will take place. In his earHer work 

 Driesch assumed from pressure experiments that the 

 egg had a great power of "regulation." In a later 

 paper' he expressed to a large extent his agreement 

 with Boveri who denied this power of "regulation" and 

 showed that the existence of the structure of the egg — 

 i. e., a division into three strata, one forming the ecto- 

 derm, the second the entoderm, and the third the 

 mesoderm — was sufficient to explain the various pheno- 

 mena of apparent "regulation." Driesch's idea of a 

 regulation in this case has often been used to insist 

 upon the non-explicability of the phenomena of de- 

 velopment from a purely physicochemical view-point. 

 It is, therefore, only fair to point out that Boveri^ 

 has furnished the facts for a simpler explanation, which 

 seems to have escaped the notice of antimechanists. ^ 



The objection may be raised that in accepting Boveri 's 

 facts and interpretation we pushed the miracle only 

 one step farther and that we now have to explain the 

 origin of the structure in the unfertilized egg. This 



^ Driesch, H., Arch. f. Entswcklngsmech., 1902, xiv., 500. 



^ Boveri, Th., Verhandl. d. physik. med. Gesellsch., Wtirzburg, N.F., 

 1901, xxxiv., 145. 



^v. Uexkull makes in his last book {Bausteine zu einer hiologischen 

 Weltanschauung, Munchen, 1913, p. 24) the following statement: 

 " Driesch suceeded in showing that the germ cell has no trace of a 

 machine-like structure but consists entirely of equivalent parts." This 

 is not correct. 



