PHYLOGENY AND ONTOGENY OF NEURONA 61 



psychic denomination. The body of the cell shows 

 the necessity of extending and multiplying its sur- 

 face. Its wealth in prolongations from the trunk 

 is extraordinary ; and if we remember that we are 

 considering the brain of a child a few days old, one 

 can imagine how important is the increase of pro- 

 longations in an adult. 



The central prolongation is little seen in this 

 diagram, but it goes on multiplying its ramifica- 

 tions in consonance with that of the trunk of the 

 neurona. 



The peripheric prolongation appears splendidly 

 here ; the shoot is very large, and terminates in 

 the cerebral surface, spreading out into a magnifi- 

 cent tuft. The diagram explains more than any 

 description. 



Ontogeny 



The history of the embryonic evolution of the 

 neurona in the same individual, the various and 

 successive phases by which it arrives at a definite 

 state, is what we call the ontogeny of the neurona. 



The study of ontogeny is transcendental, because 

 the evolution pursued by the human neurona 

 during the nine months of gestation corresponds to 

 the phylogenic evolution by which the neurona 

 passes from the gastrula through the whole animal 

 kingdom up to man. That is to say, that, as 



