48 L. S. ROSS 
periphery of the cell, the cone usually being rather sharply 
differentiated from the cytoplasm immediately in contact by 
the absence of Nissl substance. Only as a name, other than 
descriptive, can the term axone hillock be used in connection 
with the large nerve cell of the arthropod (Dahlgren and Kepner, 
’08), for the reason that the axone has an intracellular origin 
and a course almost or quite enveloping the nucleus. 
In the large cells of the abdominal ganglia of the crayfish 
the evident origin of the axone is not a definite implantation cone, 
but rather it is a band or tract of some width curving about the 
nucleus and composed of numerous fibrillae originating in all 
parts of the cytoplasmic mass (figs. 1 to 8, 10, 12,14 to 21). The 
main portion of the tract as it curves about the nucleus usually 
lies at a little distance from it, although in a few cells observed, 
in a plane of section parallel with the curve of the long axis of 
the tract, it not only touches the nucleus, but produces a very 
marked indentation without any break in the nuclear membrane 
(figs. 2 to 5 and 7). This cannot be an artefact produced by 
knife pressure, as there is no indication whatever of tearing of 
the ganglia; and also the indentations do not occur in an isolated 
section, but rather in several sections of series in different cells. 
At the place of contact there is no evidence of continuity of the 
tract with the nucleus. In some of the cells the compact en- 
circling portion of the intracellular axone is very broad and 
trough-shaped or cup-like with the nucleus situated in the 
depression of the trough. Figures 20 and 21 show extreme 
widening; these sections are consecutive, showing one limb of the 
cut tract on one side of the nucleus and ‘the other limb on the 
opposite side. Other sections in the series make it evident that 
the two limbs as shown are parts of the one greatly broadened 
tract. Figure 10 indicates a similar condition in another cell, 
while figures 17 to 19 show a sharp angle between the two limbs. 
Only three cells of the large numbers observed indicated such an 
extreme widening of the compact portion of the tract. Possibly 
sections of some of the cells in planes other than those followed 
might have made such a widening evident. 
