160 BULLETIN OF THE 
two definite lines whose significance will be considered later. (Cf. Plate 
VI. Figs. 72-88.) 
The large ganglion cells so far surpass in size those of the first kind 
that they might well be called giant cells were it not that the name 
implies a homology which I do not wish to affirm. There are in all 
five pairs of these large cells, which are nearly constant both in position 
and in size. Figure 94 (Plate VIII.) represents them diagrammati- 
cally and from a comparison of this with Figure 63 (Plate V.) the dif- 
ferent cells may be recognized at once. It will be convenient in the 
description to designate them by numerals, beginning with the most 
anterior pair. 
Since the chief characteristic of the cells of the second class taken as 
a whole is the nucleus, I shall begin with a description of this struc- 
ture, which is relatively very large and somewhat irregular in form 
(Plate V. Fig. 69). It never stains deeply, and shows one or more clear 
vacuolated areas. The nuclear membrane is delicate, and the chromatic 
substance finely distributed in lines or rows of dots. The nucleoli vary ; 
sometimes (Pl. VII. Fig. 95, cl. gn. III.) none are present, and again 
there are (Fig. 95, cl. gn. V.) one or two very prominent ones, or in 
other cases (Pl V. Fig. 69) a number of smaller ones. Frequently, one 
finds within the nucleus structures (Fig. 69) of an irregular appearance 
surrounded by a clear space of varying width, and bounded externally 
from the surrounding nuclear matter by a very definite line. It ap- 
pears as if the irregular bodies had originally filled the clear space or 
vacuole, and had shrunken away from the enveloping nuclear matter in 
the process of preservation. Exactly similar structures occur in the 
nuclei of the dorsal cells to be described, as well as in the nuclei of the 
large cells in the anal ganglion: whatever the nature of these enclosures 
may be, they seem to be characteristic at least of the larger ganglion 
cells. Ido not know that similar bodies have been found in ganglionic 
cells of other animals. 
The amount of protoplasm which surrounds the nucleus in the five 
pairs of large ganglion cells varies, somewhat in relation to the position 
occupied by the cells. The cells of the most posterior pair (Tig, 95, 
cl. gn. V.), which protrude above the mass of the brain, have a consid- 
erable amount of cell protoplasm; those of the third pair (Fig. 95, 
cl. gn. III), which are only partly surrounded by fibres, show a lesser 
quantity, while the others, which are deeply embedded in the fibrous 
substance, have merely a thin mantle of protoplasm surrounding the 
nucleus. 
