NERVE CELLS OF THE CRAYFISH AZT 
conclude that it is highly improbable that the neuroplasm of the 
crayfish nerve cell contains either a fine or a coarse network such 
as is revealed by the majority of neurofibrillar methods. As 
Heidenhain (’11) has pointed out, the killing fluids used for 
silver and gold neurofibrillar methods are poor protoplasmic 
fixatives. The same may be said of ammonium molybdate, 
ammonium picrate, nitric acid and aqueous mercuric chloride. 
In the latter case very different pictures are obtained when one 
does not treat the material first with iodine and then with 
pyridine as Donaggio did. The least that we can say is that the 
existence of a cytoreticulum and the supposed relation of neuro- 
fibrillae to a perinuclear net rest upon insecure foundations. 
The use of the term reticulum or reticulation in this paper is 
for convenience and does not commit the author to the opinion 
that a reticulum exists in living protoplasm. 
In his work upon the Crustacea, Retzius (90), pone upon 
insufficient evidence, reaches the conclusion that the large 
nerve cells, which are considered in this paper, are motor and 
the small ones are sensory. Dolley (’13) considers the cray- 
fish nerve cells as divided into two principal groups, the motor 
and the sensory, the principal differentiating characteristic being 
the presence of an ‘intracellular axone’ in the former. On 
the other hand, Allen (’94) considers that the cells within the 
ganglionic chain are motor and coordinating and that the sensory 
cells lie outside the chain. The cells without the ‘intracellular 
axone’ are much more numerous than those possessing it. 
Let us turn now to my own observations. The general form 
of the large cell of the crayfish is pear-shaped with the axone 
leaving the narrow end, the transition into the extracellular 
axone being gradual rather than abrupt. Not unfrequently the 
diameter of the axone, about one-fifth to one-fourth the diameter 
of the cell body, may be slightly greater near the exit from the 
cell than it is immediately outside. In some instances the axone 
is almost, straight at its exit, while in other cases it shows 
distinctly short, sharp undulations (fig. 7). 
In many nerve cells, especially in vertebrates, the gross origin 
of the axone is in the axone hillock or implantation cone near the 
