So he is very careful to keep the front door closed. This he does by stopping it up with leaves, leaf stems, and sticks. He also protects the door with little heaps of smooth round pebbles; but these pebbles are of a larger size than those he uses for paving the floor of his chamber. Besides helping to keep out drafts these pebbles serve another purpose. As our ancestors, the cave-builders, barred the door with boulders to keep out bears and other unwelcome callers, so the earthworms are protected by the pebbles, to a certain extent, from one of their enemies--the thousand-legged worm. Because of these little forts, the earthworms can remain with more safety near the doorway and enjoy the warmth of the morning sun. (So we might have reproduced Corot's "Morning" as a kind of landscape the earthworm enjoys!)
From all of which you can see the earthworm, for what small schooling he gets, is a very bright boy! If we were as bright, according to our opportunities, we would probably have answered long ago such puzzles as the question whether there is really anybody at home in Mars, how to keep stored eggs from tasting of the shell, and other great scientific problems of our day.
Just as we have little brains in the tips of our fingers, the earthworms have brains in the ends of their "noses." They have neither eyes nor ears, but, like that wonderful girl, Helen Keller, they make up for the lack of these senses, to a remarkable degree, by the development of the sense of touch. They acquire quite a little knowledge of Botany, for example. They not only know that leaves are good to eat, but they know which is the "petiole" and which is the "base." They always drag leaves into their burrows by the smallest ends, because this makes it easier to get them through the door. And it is not by mere instinct that they do this. Supply worms with leaves of different form from those which grow in the region where they live, and they will experiment with them until they find just the best way in which to pull them into the burrows. After that they will always take hold of them so, without further experiment. That is the majority of them will do this; for earthworms are like other little people--all of them are not equally ambitious or studious.