Reflex action, the mechanical sympathy, if I may so call it, of distant parts; Instinct, which is crystallized intelligence,—­an absolute law with its invariable planes and angles introduced into the sphere of consciousness, as raphides are inclosed in the living cells of plants; Intellect,—­the operation of the thinking principle through material organs, with an appreciable waste of tissue in every act of thought, so that our clergymen’s blood has more phosphates to get rid of on Monday than on any other day of the week; Will,—­theoretically the absolute determining power, practically limited in different degrees by the varying organization of races and individuals, annulled or perverted by different ill-understood organic changes; on all these subjects our knowledge 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