HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 99 
arranged loosely in concentric layers. The inner fibres seem to be em- 
bedded in the cytoplasm of the cell. 
(6) Although the remaining cells (Figs. 16, 17) present a great vari- 
ety of size, form, and detail of structure, there is a gencral similarity 
which permits of classing them together as a group distinct from those 
we have described thus far. They have the pear shape and the granu- 
lar eytoplasm which are characteristics of most of the cells of the 
ventral ganglia. But beyond this there is little that is common to 
all the cells of the group. In the posterior half of the brain there are 
several pairs of very large cells which have the characteristics of this 
group, and in addition a very striking one of their own. The nucleus 
lies in the narrow end of the cell, and is surrounded by the granular 
cytoplasm. At the other end of the cell, there is a large vacuolar space 
containing a number of deeply staining bodies of irregular form, em- 
bedded in an indistinct coagulum. Other cells have very finely granular 
substance occupying a similar position, the granules being much 
smaller and staining less deeply than those of the body of the cell. 
In these cases the nucleus shows no signs of degeneration. In some 
cells (Fig. 16) the cortical part of the cytoplasm is penetrated by narrow 
lamellæ, which, when viewed from the surfaces of the cell, present the 
appearance of a honeycomb structure. 
There is another structure within the brain capsule which is very 
strange, and for which I cannot account. It consists of a considerable 
number of spheroidal cavities (Fig. 10), containing a substance which 
assumes several forms. The cavities are arranged in two symmetrical 
groups, one on each side of the brain (Fig. 9), extending around and 
between the fibres of the fourteenth nerve, and backward and outward 
to the root of the thirteenth nerve. The cavities, which are surrounded 
by neuroglia, vary somewhat in size, the average being about equal to 
that of the average nerve cell of the brain. Each usually contains a 
number of spherical granules, sometimes of nearly uniform sizo, some- 
times differing much in this respect. They are stained in iron-hema- 
toxylin, but in preparations treated with osmic acid thoy are yellow, 
Sometimes the cavities are filled with an almost homogeneous substance ; 
at other times, however, the substance only partially fills the cavities, and 
assumes an irregular stellate form. In a few cases there are doubtful 
indications of a nucleus. 
These structures cannot be due to degeneration of nerve cells, because 
they are very regular in the place of their occurrence, and there is no 
indication of degenerated fibre tracts. The contents of the cavities are 
