PHYLOGENY AND ONTOGENY OF NEURONA 63 



Resuming the study of phylogeny in the animal 

 world, it originates in a cellular organism which 

 terminates in man ; and the ontogenic evolution of 

 the same man takes its origin from a cellular 

 organism like the ovule, so as to terminate its 

 evolution at the nine months in the child. The 

 difference between phylogeny and ontogeny lies in 

 the time in which they take place. 



In fig. 12, which represents the embryonic period 

 in a vertebrate, the elements of the neuronas are 

 found to appear in the same chronological order in 

 which they showed themselves in the animal or 

 phylogenic series. In a, we see a periform cell and 

 an undivided prolongation : this phase is called the 

 neuroblastoderm of His. In b, we see the peripheric 

 prolongation ; in c, the peripheric prolongation 

 extends to the form of a shoot. In d, its trunk 

 appears with a protoplasmic expansion, the central 

 prolongation begins to branch out, and the peri- 

 pheric prolongation prolongs its shoot still more. 

 In 0, the same features appear much more pro- 

 nounced. 



Fig. 13 represents the ontogenic series after 

 Kolliker, studied in a human embryo, and one sees 

 that the progression and differentiation are the 

 same. 



In this sketch (fig. 13) we see three young cells 

 of a human embryo about 23 centimetres long. 



