PSYCHIC GRADATIONS. 113 



IV. — The fourth stage is characterised by the 

 centralisation or integration of the nervous system, 

 and, consequently, of sensation ; by the association 

 of the previously isolated or localised sensations 

 presentations arise, though they still remain uncon- 

 scious. That is the condition of many both of the 

 lower and the higher animals. 



V. — Finally, at the fifth stage, the highest psychic 

 function, conscious perception, is developed by the 

 mirroring of the sensations in a central part of the 

 nervous system, as we find in man and the higher 

 vertebrates, and probably in some of the higher 

 invertebrates, notably the articulata. 



All living organisms without exception have the 

 faculty of spontaneous movement, in contradistinction 

 to the rigidity and inertia of unorganised substances 

 {e.g., crystals) ; in other words, certain changes of 

 place of the particles occur in the living psychoplasm 

 from internal causes, which have their source in its own 

 chemical composition. These active vital movements 

 are partly discovered by direct observation and partly 

 only known indirectly, by inference from their effects. 

 We may distinguish five stages of them. 



I. — At the lowest stage of organic life, in the chro- 

 macea, and many protophyta and lower metaphyta, 

 we perceive only those movements of growth which are 

 common to all organisms. They are usually so slow 

 that they cannot be directly observed ; they have to 

 be inferred from their results — from the change in 

 size and form of the growing organism. 



II. — Many protists, particularly unicellular algae of 

 the groups of diatomacea and desmidiacea, accomplish 

 a kind of creeping or swimming motion by excretion, 

 or by ejecting a slimy substance at one side. 



I 



