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 animal 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 incertcz 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. MASTIGOPHORES. SARCODINES. SPOROZOA. 



Ciliates Flagellates. Rhizopods. Gregarinida. 



Suctoria (Suckers) Choanoflagellates. Heliozoa. Coccidia. 



Dinoflagellates. Radiolarians. Sarcosporidia. 



Cystoflagellates Myxosporidia. 



Microsporidia. 



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. 



