PSYCHIC GKADATIONS. 117 



construction of the reflex mechanism is the division into 

 three cells; in the place of the simple connecting 

 bridge we spoke of there appears a third independent 

 cell, the soul-cell, or ganglionic cell ; with it appears 

 also a new psychic function, unconscious presentation, 

 which has its seat in this cell. The stimulus is first 

 conducted from the sensitive cell to this intermediate 

 presentative or psychic cell, and then issued from this 

 to the motor muscular- cell as a mandate of move- 

 ment. These tricellular reflex organs are preponderantly 

 developed in the great majority of the invertebrates. 



VII. — Instead of this arrangement we find in most 

 of the vertebrates a quadricellular reflex organ, two 

 distinct " soul-cells," instead of one, being inserted 

 between the sensitive cell and the motor cell. The 

 external stimulus, in this case, is first conducted 

 centripetally to the sensitive cell (the sensible psychic 

 cell), from this to the will-cell (the motor psychic cell), 

 and from this, finally, to the contractile muscular cell. 

 When many such reflex organs combine and new 

 psychic cells are interposed we have the intricate 

 reflex mechanism of man and the higher vertebrates. 



The important distinction which we make, in 

 morphology and physiology, between unicellular and 

 multicellular organisms holds good for their elemen- 

 tary psychic activity, reflex action. In the unicellular 

 protists (both the plasmodomous primitive plants, or 

 protophyta, and the plasmophagous primitive animals, 

 or protozoa) the whole physical process of reflex action 

 takes place in the protoplasm of one single cell ; their 

 " cell-soul " seems to be a unifying function of the 

 psychoplasm of which the various phases only begin to 

 be seen separately when the differentiation of special 

 organs sets in. 



