142 PATTEN. [Vot. II. 
finally, at some distant point, perhaps, a second vibration is 
produced exactly like the first. We may suppose that in the 
eye, light causes some change—it may be vibrations of the 
retinidial fibrille which are transmitted, not as vibrations, but 
as chemical changes, along the fibres of the optic nerve to the 
medullz, where they give rise to other vibrations exactly like 
those produced in the eye. The changes aroused in each 
retinal cell are transmitted along a bundle of wires to the 
medullz, where they are united in a proper sequence of time and 
place, which if we could see or hear, we should recognize as the 
same symphony of activities produced in the eye. An essential 
feature of the telephone is the similarity in structure and action 
of the two ends. It was the similarity in structure between 
the retina and the medullz which led me to infer that the 
activities aroused in one must produce similar activities in the 
other. 
The fibrilla at the proximal ends of the medullz unite to 
form the medullary stalk to the optic ganglion, which is con- 
tinuous with the medullary substance of the brain. The me- 
dullz of those eyes belonging to the same segment unite first, 
that is, medulla I. with II., III. with IV., and V. with VI., so 
that three stalks are formed, which almost immediately unite 
with one another to form the common stalk of the whole optic 
ganglion. Thus another intimation of the threefold structure 
of the optic ganglion is given. 
On the dorsal surface of the young larval optic ganglion are 
some small, deeply stained cells, crowded together to form 
three ill-defined clusters, one on the side and dorsal surface of 
each of the three branches of the medullary stalk. The nerve 
cells send downwards single fibrous prolongations, which, after 
uniting with one another to form ill-defined bundles (Fig. 48, 
p.n. fy, pass to the sides of the medullze where they appear to 
break up into fine fibrilla. The latter issue from the distal 
end of the medulla and immediately unite to form coarse 
fibres about the size of those which arise directly from the 
ganglionic cells. These fibres then unite in large bundles to 
form the optic nerves. 
Between the medulle are scattered cells, which in the 
younger stages cannot be distinguished from other cells in 
the brain and optic ganglion. 
