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came conscious of that which had heretofore been an unknown world.

It is necessary to touch upon the embryology of the eye only for its psychological bearing, that is, the development of sight. Notice then that the sensitive area becomes depressed, then cupped. This shape protects better and also increases the recognition of direction. For greater protection the cavity becomes closed and the cornea and lens develop. For what purpose? Evidently to collect the scattered rays of light and converge them, and focus them in a minute point on the retina. Acute sight demands perfect focusing.

Now let us apply the general law of sense perception and the outward reference of sensation to one of the psychological problems of sight, one which has been very generally misinterpreted.

The Inverted Image. It is well known that the image on the retina is inverted. How does it happen that we see objects erect? The writer devoted considerable attention to this subject some years ago, ransacking all attainable literature.

Most of the physiologies agree that it is wholly the result of experience, that the child learns by touch to reinvert the retinal picture. Foster's explanation is as follows:

"As a matter of fact the field of vision, in one important particular, does not correspond to the field of external objects. The image is inverted. The rays of light proceeding from an object which by

touch we know to be on what we call our right-hand fall on the left-hand side of the retina. If, therefore, the field of vision corresponded to the retinal image the object would be seen on the left hand. We, however, see it on the right hand, because we invariably associate right hand tactile localization with left hand visual sensation. That is to say, the field of vision, when interpreted by touch, is a reinversion of the retinal image."

I

Martin, in his work on " The Human Body," says: "A new-born child, even supposing it could use its muscles perfectly, could not seize a reachable object which it saw. It would not yet have learned that attaining a point exciting that part of the retina above the fovea (center) meant reaching a position in space below the visual axis; but very soon it learns that things near its brow, that is, up, excite certain visual sensations, and objects below its eyes, others; and learns to interpret retinal stimuli, so as to localize accurately the directions, with reference of its eyes to outer objects, and never henceforth gets puzzled by retinal inversion."

These two statements are fairly representative, and altho clear and lucid, are not only inadequate, but

erroneous.

First. This reversal by one sense, the tactile, of the testimony of the outer world, as given by another sense, the visual, is not analogous to the other special senses; and during the learning lapses would

'Physiology.

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occur and pathology would furnish instances of mistakes.

Second. Certain forms of congenital blindness, such as cataracts and complete closure of the pupil, can be remedied by operation. These children learn by touch the correct (erect) position of objects, and their first impression when sight is restored would be an inversion of the object, according to the current theory. As far as the author knows no case of this kind has ever been recorded.

cataracts.

Dr. J. L. Minor, Memphis, Tenn., reported to the writer in November, 1898, two cases of congenital The patients were brothers between thirty and forty years of age, and had never seen. After removing the cataracts the doctor kept these men under observation for a month, and assures us "there was never even a suggestion of inverted images."

The case of Rev. Mr. Hanna, reported by Sidis, who after falling from his carriage lost all memory of his former life experience, is a unique bit of evidence. He was as a newly born infant opening his eyes for the first time on the world. So totally obliterated from memory were the experiences of his past life that even the simplest mental processes, like the appreciation of distance, form, size, and magnitude, were effaced from his mind, but objects were seen erect.

Mr. Hanna's subsequent statement is as follows: The eyes suddenly opened quite involuntarily,

and here indeed was a new world of wonder and study. Objects were all alike as to distance, shape, and thickness, but the variety of color was the feature of interest. The room was a great beautiful picture, absolutely without movement or distance beyond the eye." I

Furthermore, this is a misconception, based on the old theory of special immediate creation of perfected organisms, and finds no place in the scientific thought of to-day. It is inconsistent with the facts of evolution, which means a regular progression from the simple to the relatively complex; and the explanation of the phenomena of sight must cover the primitive eye, as well as the perfected organ.

The function of the primitive eye must have been limited to simple sensitiveness to light, and the implication of the law of natural selection, that every minute change which was continued was of greater advantage to its possessor than a preceding stage, absolutely excludes the tactile reinversion theory. The specialization of a sense organ in such a way that its evidence of the outer world was misleading (inverted) until corrected (reinverted) by some other sense organ (touch), could not have been of more advantage to its possessor than a less highly developed organ which could be trusted; and natural selection would have carefully avoided propagating any such variation.

The inversion is an accomplished fact as soon as 'Sidis: Multiple Personality.

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the primitive eye is able to locate an external point in space, for it can never see the point till it can tell its direction.

The subsequent changes are all along this line of so perfecting the mechanism that a luminous point in space shall produce an irritant point on the retina. Thus there is no break in the contemporaneous development of the organ of seeing and the psychical act of seeing. They advance with equal step. There is no catastrophe; no period when the optical apparatus gives wrong impressions to the sensory.

It is indeed strange that ophthalmologists have so universally neglected to elucidate this puzzling phenomenon, and in what follows the author is borrowing from Le Conte, whose explanation is the only satisfactory one which has come to his notice.

A cone of light emitted by a radiant point falling on a convex refracting surface is again converged to a point behind the refracting surface. These two points are called conjugate foci (literally yoked together), because if the radiant be placed at either focus the light will be brought to a point at the other focus. (Fig. 1.)

FOCUS

FOCUS

FIG. 1.-CONJUGATE FOCI.

In the normal eye, at rest, a luminous point twenty feet or more distant is focused as a point on the