186 OUTLINES OF EVOLUTIONARY BIOLOGY 



organism may be altered without altering the movements going 

 on in a particular part of it, is to hold that these movements will 

 not be affected by the altered distribution of forces ; and to hold 

 this is to deny the persistence of force." 1 



In other words, the whole complex system of forces which 

 determines the constitution of the germ cells must be in a state 

 of equilibrium with the system of forces which determines the 

 constitution of the body, and any disturbance in the latter must 

 be met by a corresponding disturbance in the former. The same 

 idea may be expressed by saying that modifications of the soma 

 act as stimuli, which make more or less permanent impressions or 

 "engrams" upon the germ cells in much the same way that 

 * stimuli of various kinds received through the sense organs make 

 impressions upon certain cells in the brain." 1 > In the case of the 

 brain cells the original impressions may become dormant and be 

 revived later on as memories, which are a kind of reproduction 

 of the phenomena to which the impressions were originally due. 

 In the case of the germ cells it is supposed that the engrams also 

 become dormant, but are aroused to activity again in the course 

 of the development of these cells into new organisms, exerting 

 their influence in such a manner as to bring about a kind of 

 reflection, in the body of the offspring, of the parental characters. 

 This is the central idea of the "Mnemic" 2 theory of heredity, 

 associated more especially with the names of Hering, Samuel 

 Butler 3 and Semon. 4 



/ According to some authorities it is through a continuity of 

 protoplasm from cell to cell, or especially through the nervous 

 system in the case of the higher animals, that stimuli are trans- 

 mitted from the soma to the germ cells, but the assumption of 

 any definite material paths for such transmission seems an 

 altogether superfluous encumbrance of the theory. 



It has long been known that it is possible to send messages, or if 

 we like to call them so, stimuli, from one place ifo another without 

 any material means of communication. The very existence of 

 life on the earth depends upon stimuli received in the form of 



4 l " Principles of Biology " (London, 1881), Vol. II., p. 387. 



2 From the Greek ju.vniJ.ri, memory. 



See Butler's "Life and Habit" (2nd Edition, London, 1878) and "Un- 

 conscious Memory " (New Edition, London, 1910), the latter of which contains a 

 translation of Bering's lecture " On Memory as a Universal Function of Organized 

 Matter." 



* Semon, " Die Mneme als erhaltendes Prinzip im Wechsel des organischcn 

 Geschehens," 3rd Ed., Leipzig, 1911. 



