The Dawn of Reason; or, Mental Traits in the Lower Animals

by Jr. James Weir

Jelly-fish seek the light, and they can be made to follow a bright light from one side of the aquarium to the other by manipulating the light in the proper manner. Even where a slight current is set up in the water, they will swim against it in their efforts to reach the light.

When two or more of the marginal bodies are excised, no effect seems to follow such excision, but as soon as the last of these bodies is cut out, the creature falls to the bottom of the tank without motion.

When a point in the nectocalyx is irritated with a point of a needle or by a vegetable or mineral irritant, the tip of the manubrium will turn toward, and endeavor to touch, the spot irritated. It does not turn at once, as it would were its movements the result of reflex action; it moves deliberately as though actuated by volition.

The above experiments and observation seem to indicate the presence of conscious determination in the medusa; in fact, there seems to be a distinct element of choice in these psychical manifestations.

While engaged in watching a water-louse, I saw it swim to a hydra, tear off one of its buds, and then swim some distance away to a small bit of mud, behind which it hid until it devoured its tender morsel. Again it swam back to the hydra and plucked from it one of its young; again it swam back to the little mud heap, behind which it once more ensconced itself until it was through with its meal. When we remember that this little creature was among entirely new surroundings (for I dipped it from a pond in a tablespoon full of water which I had poured into a saucer), we will appreciate the fact that the water-louse evinced conscious determination and no little memory. It probably discovered the hydra accidentally; it then, as soon as it had secured its prey, swam away, seeking some spot where it could eat its food without molestation. But when it sought the hydra again and swam back to its sheltering mud heap, it showed that it remembered the route to and from its source of food supply and its temporary hiding-place.

At the base of a large terminal ganglion in the neuro-cephalic system of the common garden snail, lying immediately below and between its two "horns," will be found, I am satisfied, the centre governing its sense of direction. For, when this portion of this ganglion is destroyed, the snail loses its ability of returning to its home when carried only a short distance away; otherwise, it can find its way back to its domicile when taken what must be to it a very great distance away, indeed. Beneath the stone coping of a brick wall surrounding the front of my lawn, and which, on the side toward my residence, is almost flush with the ground, many garden snails find a cool, moist, and congenial home. Last summer I took six of these snails, and, after marking them with a paint of zinc oxide and gum arabic, set them free on the lawn. In time, four of these marked snails returned to their home beneath the stone coping; two of them were probably destroyed by enemies. Again, the same number of snails were marked, after the base of the above-mentioned ganglion had been destroyed, and likewise set free. Although they lived and were to be observed now and then on the trees and bushes of the lawn, none of them ever returned to the place from which they were taken beneath the stone coping. I have performed this experiment repeatedly, always with like results.

These experiments show that the snail is capable of conscious effort; furthermore, they indicate that this little animal is the possessor of a special sense which many of the higher animals have lost in the process of evolution. I refer to the sense of direction, or "homing instinct," so-called, which will be treated at length in the chapter on Auxiliary Senses.

Darwin has very beautifully demonstrated the senses of touch, taste, and smell in the angle-worm; provisionally he denies it, however, the senses of sight and hearing.[32] I think he is in error as to these last two senses.

Angle-worms are nocturnal in their habits, hence, we should expect, from the very nature of things, to find them able to differentiate between light and darkness. And experiments show, very conclusively, that they are very sensitive to light. My vermicularium is made of glass, consequently, when one of its inmates happens to be next to the glass sides, which very frequently occurs, it is easy to experiment on it with pencils of strong light. If a ray of light is directed upon an angle-worm, it at once begins to show discomfort, and, in a very few moments, it will crawl away from the source of annoyance, and hide in some tunnel deep in the earth of the vermicularium. Again, when the worms are out of their tunnels at night, a strong light shining on them will at once cause them to seek their holes.

If the back of an earthworm be examined with a high-power lens (×500), small points of pigment will be seen here and there in its dorsal integument; these, I believe, are primitive eyes (ocelli). I think that the worm is enabled to tell the difference between light and darkness through the agency of these minute dark spots, which serve to arrest the rays of light, thus conveying a stimulus to nerve-fibrils, which, in turn, carry it to the sensorium.