144 PATTEN. [ VoL. II. 
in Figs. 40 and 41, a fair idea will be obtained of the structure 
of the optic ganglion at the close of the larval period. 
Optic Nerves. —In the younger embryonic stages, the fibres 
connecting the eyes with the optic ganglia are so intermingled 
with ganglion-cells that it is not easy to distinguish them from 
the optic ganglion. Even in the larval stages, when the optic 
ganglion is situated behind and some distance away from the 
eyes, the optic nerves are in places so ill-defined that it is 
difficult to follow them to the medullz from which they arise. 
The nerve to eye V. descends from the outer anterior edge of 
the optic ganglion, and after reaching the inner lower edge of 
eye III. turns nearly at right angles and runs forward to join 
the eye on its posterior dorsal face. 
Nerve 6 is the most compact of all. Its root lies on the 
inside of that belonging to eye V. The two nerve roots extend 
downwards nearly parallel with each other to the lower edge of 
the ganglion; and then nerve 6 bends backwards, and sweeping 
around the lower posterior edge of eye I., terminates on the 
posterior edge of eye VI. 
Nerves I and 3 extend downward and forward from the lower 
anterior edges of their respective medullz as two great sheets 
of loose fibres. At the lower, inner edge of eye I., those of 
nerve I unite to form a more compact mass which suddenly 
bends outward and divides into five bundles, two of which run 
along the under side of the eye on either side of the retinal 
furrow. Two other bundles extend upward on either side of 
the vertical furrow. The fifth bundle extends upward to the 
dorsal appendage (Fig. 18). 
The nerve to eye III. is similar to that of eye I. in shape 
and in the direction it follows. On reaching the eye it divides 
into two branches which extend parallel with each other along 
the under side of the retina. 
In both eyes I. and III., fibres extend along the median under 
surface of the horizontal retinas, and finally bend upward to 
form, between the rows of gigantic cells, the vertical fibres. 
There is nothing noteworthy about the course of nerves 2 
and 4. 
The relative positions, in the full-grown larva, of the nerves, 
the medullz, and the eyes, throw some light on the relation of 
the eyes to one another. 
