On the Mechanical Conception of Nature. 637 



in the organic world. If such a power exists it 

 must be the inciting cause of organic develop- 

 ment in general, and must be equally necessary in 

 every part of creation, as no advancement could 

 take place without it. In this case, however, the 

 force would be recognizable and demonstrable at 

 every point ; the phenomena should nowhere stand 

 in opposition to its admission, and should in no 

 case be explicable or comprehensible without it. 

 The same laws and forces which caused the de- 

 velopment of one group of forms must underlie 

 the development of the whole organic world. 



I therefore believe that we are correct in ap- 

 plying to the whole living world the results fur- 

 nished by the investigation of insects, and in thus 

 denying the existence of an innate metaphysical 

 developmental force. 



There is, however, a quite distinct method 

 which leads to the same results, and to the pre- 

 liminary, if not to the complete and definitive 

 rejection of such a principle ; the admission of this 

 power is directly opposed to the laws of natural 

 science, which forbid the assumption of unknown 

 forces as long as it is not demonstrated that 

 known forces are insufficient for the explanation 

 of the phenomena. Now nobody will assert that 

 this has in any case been proved ; the test of 

 applying the known factors of transformation has 

 only just commenced, and wherever it has been 

 made they have proved sufficient as causal forces. 



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