2 THE PSYCHIC LIFE 



stands to reason. If a natural classification is always 

 a complex piece of work in the case of the higher ani- 

 mals which differ from each other in important features 

 and between which a comparison can be instituted, 

 the difficulty attending the classification of simple or- 

 ganisms which present only the slightest differentia- 

 tions is still more difficult. 



The principal division made is that which divides 

 them into anirnal Micro-organisms or Protozoans and 

 vegetable Micro-organisms or Microphytes. 



The line of demarcation between these two king- 

 doms is far from being well defined; there are a great 

 number of micro-organisms incertce sedis, which bota- 

 nists usually place in the vegetable kingdom, but which 

 zoologists prefer to classify as belonging to the ani- 

 mal kingdom.* 



We give below a list of the most important groups 

 of animal micro-organisms. 



ANIMAL MICRO-ORGANISMS. 

 Infusoria. RIastigophores. Sarcodines. Sporozoa. 



Ciliates Flagellates. Rhizopods. Gregarinida. 



Suctoria (Suckers) Choanoflagellates. Heliozoa. Coccidia. 



Dinoflagellates. Radiolarians. Sarcosporidia. 



Cystoflagellates. Myxosporidia. 



M icrosporidia. 



We propose, now, to study the psychic life of these 

 lower organisms, or, to speak in more general terms, 

 their life of relation. It is well known that the expres- 

 sion, the life of relation, comprehends essentially two dis- 

 tinct ideas: first, the action of the external world felt 

 by the organism: or sensibility; secondly, the reac- 

 tion of the organism on the external world: or move- 



*The best mark to distinguish the two kingdoms is the chemical nature of 

 the enveloping membrane: in the case of vegetable organisms, the enveloping 

 membrane is made up of a ternary substance, cellulose: while in animal organ- 

 isms it is albuminoid in character. 



