existence almost as long as life.

It is quite probable that it is to be found in the very lowest animal organisms; and, if our own senses were acute enough, it is more than probable that we would be able to demonstrate its presence, beyond peradventure, in such organisms.

The senses of taste and smell, according to Graber, Lubbock, Farre, and many other investigators, seem to be almost as old as the sense of touch. My own observations teach me that certain actinophryans,[5] minute, microscopic animalcules, can differentiate between the starch spores of algæ and grains of sand, thus showing that they possess taste, or an analogous sense.

On one occasion I was examining an actinophrys (Actinophrys Eichornii), which was engaged in feeding. It would seize a rotifer (there were numerous Brachioni in the water) with one of its pseudopodia, which it would then retract, until the captured Brachionus was safely within its abdominal cavity. On the slide there were several grains of sand, but these the actinophrys passed by without notice.

I thought, at first, that this creature's attention was directed to its prey by the movements of the latter, but further investigation showed me that this was not the case.

After carefully rinsing the slide, I placed some alga spores (some of which were ruptured, thus allowing the starch grains to escape) and some minute crystals of uric acid upon it. Whenever the actinophrys touched a starch grain with a pseudopod, the latter was at once retracted, carrying the starch grain with it into the abdominal cavity of the actinophryan; the uric acid crystals were always ignored.

I conclude from this experiment, that the actinophrys, which is exceedingly low in the scale of animal life, recognizes food by taste, or by some sense analogous to taste.

Many species of these little animals, however, are not as intelligent as the Eichorn actinophrys; they very frequently take in inert and useless substances, which, after a time, they get rid of by a process the reverse of that which they use in "swallowing." By the latter process they put themselves on the outside of an object—in fact, they surround it; by the former, they put the object outside by allowing it to escape through their bodies.

The sense of sight makes its appearance in animals quite low in the scale, therefore the reader will pardon me if, while discussing this sense, I prove to be a bit discursive. The subject is, withal, so very interesting that it calls for a close and minute investigation.

One of the immutable laws of nature declares that animals which are placed in new surroundings, not fatal to life, undergo certain changes and modifications in their anatomical and physiological structures to meet the exigencies demanded by such a modification of surroundings. Thus, the flounder and his congeners, the turbot, the plaice, the sole, etc., were, centuries and centuries ago, two-sided fishes, swimming upright, after the manner of the perch, the bass, and the salmon, with eyes arranged one on each side of the head. From upright fishes, swimming, probably, close to the surface of the sea, they became dwellers on its bottom, and, in order to hide themselves more effectually from their enemies or their prey, they acquired the habit of swimming with one side next to the ground, and of partially or wholly burying themselves in the mud, always, however, with one side down. They thus became flat fishes, losing the coloring of their under surfaces, and their eyes migrating across their foreheads and taking up positions on the upper surfaces of their heads. Again, when animals are placed among surroundings in which there is no need for some special organ, this organ degenerates, and passes wholly or partially into a rudimentary condition, or, entirely out of existence. These latter effects of changed conditions on animals are especially noticeable in the effect of continual darkness on the organs of sight of those creatures which, owing to said mutations, have been compelled to dwell in darkness for untold ages.

The mole, far back in the past, had eyes, and gained its livelihood above ground in the broad light of day; but, owing to some change in its surroundings, it was forced to burrow beneath the surface of the earth; consequently its organs of sight have degenerated, and are now practically worthless as far as vision is concerned. All moles, however, can tell darkness from light, consequently, are not wholly blind—a certain amount of sight remains. This is due to the fact that, although the optic nerve, on examination, is invariably found to be atrophied or wasted, there yet remain in the shrivelled nerve-cord true nerve-cells; these nerve-cells transmit light impressions to the brain.

Even if the optic nerves, and, in fact, all of the structures of the eye, were absent, I yet believe that the mole could differentiate between daylight and darkness. The sensitive tufts and filaments of nerve in the skin, undoubtedly, in many instances, respond to the stimulation of light, so that totally blind animals, animals with no rudimentary organs of vision whatever, and the inception of whose ancestors, themselves wholly blind, probably took place thousands of years ago, show by their actions that light is exceedingly unpleasant to them. Thus, I have seen actinophryans taken from the River Styx in Mammoth Cave (which is their natural habitat), seeking to hide themselves beneath a grain of sand which happened to be drawn up in the pipette and dropped upon the glass slide beneath the object-glass of my microscope.

I have repeatedly seen the blind fish of Mammoth Cave seeking out the darkest spots in aquaria. In point of fact, I think it can be demonstrated that light is directly fatal to these fishes; they soon die when taken from the river and placed in aquaria where there is an abundance of light.

These fish, although they have rudimentary eyes, never have the slightest remaining trace of nerve-cells in the wasted optic nerve (that is, I have never been able to discover any), thus showing that their appreciation of light is not derived through the agency of their eyes. An eyeless spider (Anthrobia) taken from the same cavern showed a like distaste for light, and yet, in this insect, there is absolutely no vestige of an eye or its nerves.

Finally, a friend of mine, a youth of eighteen, totally blind since birth, can differentiate between daylight and darkness. On one occasion I carefully blindfolded him and led him into the well-lighted office of a brewery (he had never been in a brewery before), and asked him if it were light or dark. He answered that it was almost as light as day. I then conducted him into the dark beer vaults, and as soon as he passed the door he exclaimed, "How cold and dark it is here!" Thinking that he might possibly associate darkness with coldness, I asked him if this were the case. "No," he replied, "I see the darkness and I feel the cold; they are not the same."

In these animals—and I include man—continuous darkness has modified sensibility (sense of touch) to such an extent that it has partially taken on the functions of the useless organs—the eyes; these creatures see with their skins.

I do not believe that there is a creature in existence to-day, whether it has eyes or not, which cannot tell the difference between night and day. Professor Semper says that in the Pelew Islands he found a small fresh-water creature, whose generic name is Cymothoe, in pools where daylight penetrated, that was absolutely blind.[6] We have