76 IOSNTAL EVOLUTION IN ANIMALS. 



the purposes of merely historical psychology as would be a 

 full understanding of the causal connection, if there is any 

 such connection to be understood. 



So much, then, for the physical conditions under which 

 consciousness is always and only found to occur. It remains 

 briefly to conclude this chapter by showing that these con- 

 ditions may most reasonably be regarded as first arising 

 within the limits between which I have represented the 

 origin of consciousness. 



Eemembering what has already been said concerning the 

 gradual or undefined manner in which consciousness probably 

 dawned upon the scene of life, and that I therefore represent 

 its rise as occupying a wide area on the diagram instead of a 

 definite line, I think it least objectionable to place the begin- 

 ning of this dawn in nervous adjustments or reflex action, 

 and the end of it in the association of ideas. For, on the one 

 hand, it is clear from what has been said that it is impossible 

 to draw any definite line between reflex and conscious action, 

 inasmuch as, considered objectively or as action, the latter 

 differs from the former, not in kind, but only in a gradual 

 advance in the degree of central co-ordination of stimuli. 

 Therefore, where such central co-ordination is first well 

 established, as it is in the mechanism of the simplest reflex 

 act, there I think we may with least impropriety mark the 

 advent of consciousness. On the other hand, where vague 

 memory of past experiences first passes into a power of asso- 

 ciating simple ideas, or of remembering the connections 

 between memories, there I think consciousness may most 

 properly be held to have advanced sufficiently far to admit of 

 our regarding it as fairly begun. 



In this scheme, therefore — which of course it is needless 

 to say I present as a somewhat arbitrary estimate where no 

 more precise estimate is possible — the Ccelenterata are repre- 

 sented as having what Mr. Spencer calls " the raw material 

 of consciousness," the Echinodermata as having such an 

 amount of consciousness as I think we may reasonably sup- 

 pose that they possess, if we consider how multifarious and 

 complicated their reflex actions have become, and if we 

 remember that in their spontaneous movements the neuro- 

 muscular adjustments which they exhibit almost present the 

 appearance of being due to intelligence* The Annelida I 

 * See Phil. Trans,, Croonian Lecture, 1881. 



