138 PATTEN. [VoL. II. 
roots of nerves I. and III., seen in longitudinal sections, are 
somewhat swollen and divided into two parts. 
The fibres at the ends of the nerve roots turn upwards and 
pass into the stalk of the optic ganglion. Their cut ends do 
not lie on the inner surface of the ganglion, as during the earlier 
stage (Fig. 39), but in the centre. On the ventral side are seen 
medulla 3 and sections of the roots of the nerves supplying eyes 
V. and VI. 
The next section (Fig. 45) passes through eye V., and shows 
its double nerve in longitudinal, and that of eye VI. in cross 
section. It is below the level of eyes I. and III., but shows eye 
II. and its minute nerve root with its adjacent large ganglion 
cell. , 
Fig. 47 represents a section passing through eye VI. and its 
nerve just as the latter bends at right angles. It is clothed with 
nerve cells up to the very base of the eye. 
This series of sections shows the principal features of the 
optic ganglion at this stage. The parts are lettered in a way to 
show at once their relations to the eyes. They should be care- 
fully examined and compared with Fig. 8, for a better under- 
standing of the parts will be obtained in this way than by a 
long and tedious description. 
Toward the close of embryonic life most of the nerve cells are 
situated on the dorsal surface of the ganglion, where the latter 
joins the brain. 
In Fig. 48 is represented the optic ganglion as seen in a 
cross section of an embryo about ready to hatch. The section 
passed through the head between eyes II. and IV. showing a 
little of both. Fig. 8 represents a younger embryo than the one 
we have in mind, but it serves perfectly well to show the level 
of the section. As the head is bent at right angles to the body 
in such embryos, the section would be the same as a longi- 
tudinal, horizontal one of the larval head, Fig. 10. Again, the 
section we are about to describe would cut that shown. in Fig. 
49, taken, however, from an older head, just below the crown of 
ganglionic cells on its dorsal surface. At this period, the shape 
of the medulla and the characteristic arrangement of the fibres 
in them can be studied to best advantage. 
Suppose the side of the head to which belongs the optic gan- 
glion we are describing, laid flat on the paper, opposite the 
