166 JOURNAL OF COMPARATIVE NEUROLOGY. 
nerve element may contain a greater number of neurofibrillae 
than are found entering its cell, and to show that this was due 
to the fact that many neurofibrillae may enter a neurone 
through the collaterals, and pass out either through the 
peripheral fiber or through other collaterals without entering 
the cell proper. He regards such conditions as incompatible 
with the neurone theory, because the fibrils which do not enter 
the cell can not be integral parts of it, but must be the product 
of some other cell or cells. The fibrillar structures in the 
nerve elements of both the leech and the crayfish confirm 
BETHE’S observations. From methylen blue preparations of 
the abdominal ganglion of Aséacus, certain important facts may 
be observed without the use of a high magnification. As 
ApaATHY noted in the leech, many of the nerve elements are 
paired: a large element in the right half of the ganglion has 
its fellow, similar in size, form and extent, symmetrically placed 
on the other side. More interesting still is the fact that doth of 
these paired elements usually take the stain together, indicating the 
existence of connection between them. In many of my 
preparations of the second abdominal ganglion a pair of large 
motor elements was often demonstrated. One of these from 
the left side of the ganglion is shown in Figure 10 (Plate VI) ; 
its fellow of the right side was its mirrored image even to the 
number, position and extent of the collaterals. The collaterals 
always branch to the same points in the neuropil, a fact directly 
against the assumption that a diffuse fibrillar network exists. 
For if this were the case, why should the processes of different 
neurones always pass to the same spot in the neuropil, and 
why should the nerve elements be arranged in bilateral sym- 
metry? Such an arrangement would be useless if there were a 
diffuse network of fibrillae in the neuropil, to put the dendrites 
of all the nerve elements into general communication with one 
another. 
Figure 10 also illustrates a second point, which, as we shall 
see, bears upon the fibrillar structures in the nerve elements. 
The nerve fiber reaches its greatest size in the region desig- 
nated by a, and this ts the point at which most of the collaterals 
