PSYCHIC GRADATIONS. 115 



chemical change in the environment may, in certain 

 circumstances, act as a stimulus on the psychoplasm, 

 and elicit or "release" a movement. We shall see 

 later on how this important physical concept of 

 " releasing " directly connects the simplest organic 

 reflex actions with similar mechanical phenomena of 

 movement in the inorganic world (for instance, in the 

 explosion of powder by a spark, or of dynamite by a 

 blow) . We may distinguish the following seven stages 

 in the scale of reflex action : — 



I. — At the lowest stage of organisation, in the 

 lowest protists, the stimuli of the outer world (heat, 

 light, electricity, etc.) cause in the indifferent proto- 

 plasm only those indispensable movements of growth 

 and nutrition which are common to all organisms, and 

 are absolutely necessary for their preservation. That 

 is also the case in most of the plants. 



II. — In the case of many freely-moving protists 

 (especially the amoeba, the heliozoon, and the rhizopod) 

 the stimuli from without produce on every spot of 

 the unprotected surface of the unicellular organism 

 external movements which take the form of changes of 

 shape, and sometimes changes of place (amoeboid move- 

 ment, pseudopod formation, the extension and with- 

 drawal of what look like feet) ; these indefinite, variable 

 processes of the protoplasm are not yet permanent 

 organs. In the same way, general organic irritability 

 takes the form of indeterminate reflex action in the sensi- 

 tive plants and the lowest metazoa ; in many multicel- 

 lular organisms the stimuli may be conducted from one 

 cell to another, as all the cells are connected by fine fibres. 



III. — Many protists, especially the more highly- 

 developed protozoa, produce on their unicellular body 

 two little organs of the simplest character — an organ 



