A Still Progressive Tissue. 139 



which had entered the multicellular organism ami li^ed on 

 it, but repaid for its protected situation and its refined 

 food by doing the thinking, planning, and caring for its 

 host. So greatly has the function of acquiring knowl- 

 edge ennobled the brain group of cells, raising it to such 

 divine eminence over all others, that in man it has come 

 to stand for the personality of the organism, the self, the 

 ego, the soul of the human body. 



Nerve and brain are not found in unicellular life ; at 

 least, not in the organic sense of these terms. 



From as close a study as can be made of certain simple 

 forms of multicellular creatures, which are doubtless quite 

 similar to those from which the higher multicellular forms 

 were originally developed, the first rudimentary attempt 

 to establish a nervous system consisted of a living proto- 

 plasmic thread, thrust out from one cell to another. At 

 first this would appear to have been a mere " feeler," but 

 in time it came to remain constantly extended, no longer 

 as a transient feeler, but as a permanent means of sensory 

 intercommunication between cell and cell. 



But, as multicellular creatures waxed larger, and dif- 

 ferentiation of the component cell orders began, simple 

 filaments of protoplasm, modified pseudopodia, were no 

 longer sufficient for transmitting sensation from tract to 

 tract ; whole rows or lines of cells were involved in the 

 strong currents of sensation that passed to and fro, and, in 

 time, these cells became devoted wholly to the business of 



