the masses behind by the commissure, commonly called the
optic nerve. We are prepared, therefore, to find these two little brains
in the most intimate relations with each other, as we find the cerebral
hemispheres. We know that they are directly connected by fibres that
arch round through the chiasma.

I mention these anatomical facts to introduce a physiological observation
of my own, first announced in one of the lectures before the Medical
Class, subsequently communicated to the American Academy of Arts and
Sciences, and printed in its "Transactions" for February 14, 1860. I
refer to the apparent transfer of impressions from one retina to the
other, to which I have given the name reflex vision. The idea was
suggested to me in consequence of certain effects noticed in employing
the stereoscope. Professor William B. Rodgers has since called the
attention of the American Scientific Association to some facts bearing on
the subject, and to a very curious experiment of Leonardo da Vinci's,
which enables the observer to look through the palm of his hand (or seem
to), as if it had a hole bored through it. As he and others hesitated to
accept my explanation, I was not sorry to find recently the following
words in the "Observations on Man" of that acute observer and thinker,
David Hartley. "An impression made on the right eye alone by a single
object may propagate itself into the left, and there raise up an image
almost equal in vividness to itself; and consequently when we see with
one eye only, we may, however, have pictures in both eyes." Hartley, in
1784, had anticipated many of the doctrines which have since been
systematized into the theory of reflex actions, and with which I have
attempted to associate this act of reflex vision. My sixth experiment,
however, in the communication referred to, appears to me to be a crucial
one, proving the correctness of my explanation, and I am not aware that
it has been before instituted.

Another point of great interest connected with the physiology of vision,
and involved for a long time in great obscurity, is that of the
adjustment of the eye to different distances. Dr. Clay Wallace of New
York, who published a very ingenious little book on the eye about twenty
years ago, with vignettes reminding one of Bewick, was among the first,
if not the first, to describe the ciliary muscle, to which the power of
adjustment is generally ascribed. It is ascertained, by exact experiment
with th