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. [32] Darwin, _Formation of Vegetable Mould_. 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.