ge is in its infancy, and from the study of some of them the
interdict of the Vatican is hardly yet removed.

I must allude to one or two points in the histology and physiology of
the organs of sense. The anterior continuation of the retina beyond
the ora serrata has been a subject of much discussion. If H. Muller and
Kolliker can be relied upon, this question is settled by recognizing
that a layer of cells, continued from the retina, passes over the
surface of the zonula Zinnii, but that no proper nervous element is so
prolonged forward.

I observe that Kolliker calls the true nervous elements of the retina
"the layer of gray cerebral substance." In fact, the ganglionic
corpuscles of each eye may be considered as constituting a little brain,
connected with 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 wi