PRENTISS, Weurofibrillar Structures. 167 
enter or leave the neurone; both the cell process (b) and the 
peripheral fiber (c) ave considerably smaller than the region inter- 
vening between them. ‘The greater size of this particular por- 
tion of the elements is explained when the fibrillar structures are 
studied under a higher magnification (Figure 11, Plate VI). It 
may then be observed that the fibrillae are more numerous at this 
point than in either the cell process proper, or in the peripheral 
fiber. Many fibrillae of the large collaterals (d’) pass directly to 
the periphery through the fiber c’; others, like fibril e, evidently 
enter the element through one collateral and pass out through 
another. The same condition was observed in the nerve 
elements of the leech (Figure 2, Plate V). The figure is from 
a preparation fixed in ether and stained with toluidin blue. 
The plane of section was very favorable, showing the whole of 
the cell process and short portions of the peripheral fiber and of 
two collaterals in connection with the cell. Here again an 
enlargement is found at the point where the large collaterals 
branch off. As only fibrillar structures were stained, each 
fibril could be traced with perfect distinctness; a large one (a’) 
passes directly from a collateral at @ into the peripheral fiber 6 
and is, therefore, independent of the ganglion cell. 
In the large nerve elements of the leech a fibrillar net- 
work is often found in that portion of the cell process from 
which the collaterals branch. Two such cases have been 
figured (Figures 5 and 7, Plate V). Figure 5 isa type of the 
more simple connections which exist between the fibrillae in the 
nerve elements. Three large parallel fibrillae (a, a’, a’) unite 
at the point 0; atc, a single mesh is formed, from which are 
given off several smaller fibrils that continue their parallel 
courses in the process. In this, as in all well differentiated 
molybdate preparations, the perifibrillar substance is not 
stained, and the boundaries of the nerve elements are indicated 
by the course of the fibrillae only. 
The processes of the giant ganglion cells of the leech 
often exhibit extremely complicated fibrillar networks soon 
after they enter the neuropil (Figure 7, Plate V). In Figure 7 
three large fibrillae from the longitudinal commissure unite 
