180 THE RIDDLE OF THE UNIVERSE. 



of groups of presentations, seem to me to be required 

 before the unity of consciousness is possible. 



III. Animal theory of consciousness. — All animals, 

 and they alone, have consciousness. This theory 

 would draw a sharp distinction between the psychic 

 life of the animal and of the plant. Such a distinc- 

 tion was urged by many of the older writers, and was 

 clearly formulated by Linne in his celebrated Systema 

 Naturte : the two great kingdoms of the organic 

 world are, in his opinion, divided by the fact that 

 animals have sensation and consciousness, and the 

 plants are devoid of them. Later on Schopenhauer 

 laid stress on the same distinction : " Consciousness 

 is only known to us as a feature of animal nature. 

 Even though it extend upwards through the whole 

 animal kingdom, even to man and his reason, the 

 unconsciousness of the plant, from which it started, 

 remains as the basic feature. In the lowest animals 

 we have but the dawn of it." The inaccuracy of this 

 view was obvious by about the middle of the present 

 century, when a deeper study was made of the psychic 

 activity of the lower animal forms, especially the 

 coelenterates (sponges and cnidaria) : they are un- 

 doubtedly animals, yet there is no more trace of a 

 definite consciousness in them than in most of the 

 plants. The distinction between the two kingdoms 

 was still further obliterated when more careful research 

 was made into their unicellular forms. There is no 

 psychological difference between the plasmophagous 

 protozoa and the plasmodomous protophyta, even in 

 respect to their consciousness. 



IV. Biological theory of consciousness. — It is found 

 in all organisms, animal or vegetal, but not in lifeless 

 bodies (such as crystals). This opinion is usually 



