No. I.] EVES OF ARTHROPODS. 135 
The first section (Fig. 28) passes just above the anterior edge 
of the plate, and shows the proximal ends of each ganglionic 
segment, a. g.t% 
The next (Fig. 29), passes through the first invagination, 
g.v., and the anterior end of eye V.; compare Fig. 4. At this 
niveau, the third ganglionic segment, o. ¢.°, is separated from the 
third lobe of the brain by the cephalic infolding, z. 
In Fig. 30, the section passes through the centre of the third 
segment, which is not separated by any epithelial layer from the 
exterior. At x.y. is a section of the second segment of the 
optic plate, where it dips down towards the second ganglionic 
invagination. The underlying cells, o. g.1 and o. g.2, connect 
the main part of each ganglion with the segment of the optic 
plate to which it belongs. 
In Fig. 31, the section passes through the upper edge of eyes 
V. and IIL. and in Fig. 32, through about the middle of these 
eyes. The scattering fibres uniting the eyes with the optic 
ganglion indicate the position of the future nerves. 
In Figs. 33 and 34, the sections pass through the upper and 
lower edges of eye VI., and show how the optic ganglion is here 
reduced to a chord of cells continuous with the retinal cells of 
the eye. 
After the rather confusing condition shown in the last series 
of sections, it will be a relief to find in the next (Figs. 37-39), 
a simpler arrangement. These sections are taken from a head 
a little older than that shown in Fig. 4. The first section (Fig. 
37) passes through the site of the first ganglionic invagination. 
It is now closed, but there is a depression above an inwardly 
projecting core of cells, which marks its former position, g. v.} 
It also cuts the anterior edge of the first ocular plate, showing 
a small part of the first ganglionic segment, o. 1 Two or three 
sections below this we find one (Fig. 38) which passes through 
the point ¢. v.2, Fig. 4, and consequently through about the mid- 
dle of eye I. and the anterior edge of the second ocular seg- 
ment. The third segment of the optic ganglion is still exposed 
to the exterior, 0. g.3 The outer wall of the ganglionic invagi- 
nation has completely disappeared by this time, and the edge of 
the optic plate comes squarely against the outer surface of the 
third ganglionic segment. The only part of the brain seen at 
this niveau is a section of the anterior end of the antennary lobe. 
