644 Studies in the Theory of Descent. 



observed the mode in which the heat of the 

 animal body is generated by the processes of 

 combustion going on in the blood and in the 

 tissues ; nevertheless, this is believed as a cer- 

 tainty, and a "vital force " is not invoked. 



Now the above-mentioned Darwinian principles 

 of transmutation are certainly not simple forces of 

 nature like those underlying the development of 

 the individual, z. e. chemico-physical forces, and 

 it cannot be said a priori whether in one of these 

 principles perhaps in variability or in correla- 

 tion there may not lie concealed a meta- 

 physical principle in addition to the physical 

 forces. In fact it has lately been asserted by 

 Edward von Hartmann 5 that the theory of selec- 

 tion is not a mechanical explanation, since it 

 combines forces which are only partly mechanical 

 and in part directive. 



It must therefore be next investigated whether 

 this assertion is tenable. 



6 "Wahreit und Irrthum im Darwinismus." Berlin, 1875. 



