162 JOURNAL OF COMPARATIVE NEUROLOGY. 
plasm; (3) in diseased and degenerate cells certain fibrillar 
tracts, which pass in and out through the dendrites, may remain 
intact and cannot be distinguished from normal fibrillae. Nuissv’s 
figures are schematic and, as in the text, it is difficult to sepa- 
rate fact from theory. His book, however, is of great value 
in that it discloses the weak spots in the neurone theory and 
shows that little or nothing is known of the extra-cellular ele- 
ments found in the gray substance of the vertebrate nervous 
system. Between the dendrites of the nerve cells and the 
point at which the sensory axis cylinders lose their medullary 
sheaths, there is practically a total blank in our present knowl- 
edge of the nervous elements. 
Nissi accepts as an established fact ApATuy’s hypothesis 
that the nerve elements of invertebrates are connected by a 
diffuse network in the neuropil. Not so the supporters of 
the neurone theory, who are, however, divided in opinion. By 
far the majority of them admit the existence of the neuro- 
fibrillae, but deny that there is continuity between the neurones. 
Prominent among this school are von LENHOSSEK (’g9Q), S. 
MEYER ('99), and VAN GEHUCHTEN (:00). Other neurologists, 
like WaLDEYER, HocuHE (’99) and VERWORN (:00), while ad- 
mitting that fibrillar continuity may exist, hold, and we think 
rightly, that the question of contact or continuity between the 
neurones is a side issue. They doubt the existence of fibrillar 
‘‘Gitterwerke,’’ however, and still maintain that the nervous 
system is composed entirely of cell units. 
Because of this doubt which still exists in the minds of 
many neurologists, as to certain of ApATHy’s observations, the 
writer has made a special study of the fibrillar structures found 
in the neuropil of H/zxudo, the results of which are now in press. 
The present paper furnishes further evidence as to the structure 
of the neuropil and is supplemented by a more genera! study 
of the neurofibrillae in the nerve elements of both A#udo and 
Astacus. The research was begun at the Zoological Laboratory 
in the University of Freiburg, Baden, and was completed at the 
Strassburg Physiological Institute. 
