VotuME XIII. 1903. NUMBER 3. 
THE 
JournaAL oF Comparative Neurovoey. 
THE NEUROFIBRILLAR STUCTURES IN THE GAN- 
GEA’ OR THE LEECH (AND: CRAYFISH WITH 
ESPECIAL REFERENCE TO THE NEURONE 
RHEORY. 
By C. W. PRENTIss, 
Parker Fellow in Zoéblogy, Harvard University. 
With Plates V and VI. 
A previous publication treats in detail of the fibrillar net- 
works in the neuropil of the leech. In the present paper it is 
purposed to give amore general description of the fibrillar struc- 
tures found in the nervous system of the leech and crayfish and 
to point out the relation of these structures. to the neurone 
théory. 
The neurone theory, grounded upon the fundamental re- 
searches of GuDDEN, GotGI, and His, was first formulated by 
WALDEYER (’g!) in the following words: ‘‘Das Nervensystem 
besteht aus zahlreichen, unter einander anatomisch wie gene- 
tisch nicht zusammenhangenden Nerveneinheiten (Neuronen).”’ 
As WALDEYER, VERWORN, and Nisst have shown, the all-impor- 
tant point embraced in the neurone theory is not the anatomical 
independence of the nervous elements, but the assumption that 
the nervous system is entirely composed of cell individuals. 
Whether the processes of these cells are only in contact, or by 
growing together have become continuous, is a secondary mat- 
ter. Nevertheless, on the threefold evidence of histogenesis, 
neuropathology, and histology, most neurologists maintain that 
the nervous system is composed of anatomically independent, 
cellular units. 
1. Hustogenesis. That the nerve elements develop from 
single neuroblasts and not from chains of cells was first asserted 
