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part. The action and interaction of the various fac- 

 tors, however, are so complex, that it is extremely 

 difficult to determine precisely the exact part played 

 by each one of them. And this is probably the reason 

 why the authors of the various theories have yielded to 

 the temptation of ascribing to some one factor a pre- 

 ponderant role and of underestimating the importance 

 of the others. 



That exclusiveness was a source of weakness. We 

 personally think that the problem will be solved as 

 soon as we succeed in determining accurately the part 

 played by every single factor; and then, only one 

 more thing will have to be discovered, that is, the actual 

 processus of the transmission of acquired characters. 

 Then we will have an answer ready for the most em- 

 barrassing objections. 



