GROWTH AND REPRODUCTION 55 



ment or ontogeny into connection with definite 

 physiological processes and is compelled to resort 

 to a theory of determinants (or " archetectomic 

 sprites," as Francis Darwin has aptly dubbed them) 

 which is complicated and unconvincing. Moreover, 

 if one believes, as many biologists do, that the somatic 

 cells are physically continuous with the germ cells 

 and are endowed with the same kind of reproductive 

 qualities (as seen in the phenomenon of regenera- 

 tion), the Weismann hypothesis does not give us an 

 entirely satisfactory explanation of heredity. 



Let us therefore survey briefly the mnemic hypothe- 

 sis, in order to see what help it can give us. Accord- 

 ing to the German naturalist Semon (who has 

 elaborately developed the ingenious theory designed 

 by Hering to account for the hereditary qualities of 

 living organisms), stimuli or irritatives of various 

 kinds leave quite definite and permanent traces on 

 the protoplasm of the living animal or plant. Such 

 a trace, representing the reaction of the living proto- 

 plasm to the stimulation, he calls an engram. This 

 permanent physical or chemical change in the living 

 machine which results from the action of stimuli 

 has been called the " internal condition," or "physi- 

 ological state," by other investigators at least 

 there is a rough correspondence between these terms 

 and Semon's engrams. Now the essential pecul- 

 iarity of the states expressed by all these terms is 

 the regulative influence exerted on the behavior of 

 organisms even after the original external agencies 



