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This habit of lying near the surface leads to their destruction to an immense extent, for, at certain seasons of the year, the robins and blackbirds that visit our lawns in the country may be observed drawing out of their holes an astonishing number of worms, which could not be done unless they lay close to the surface. But what brings the worms to the surface? This is a question whose answer cannot be positively asserted. It is not probable that they behave in this manner for the purpose of breathing fresh air, for it has been seen that they can live a long time under water. That they are there for the sake of warmth, especially in the morning, is a more reasonable supposition, which seems to be confirmed by the fact that they often coat the mouths of their burrows with leaves, apparently to prevent their bodies from coming into contact with the cold, damp earth, and by the still other fact that they completely close their burrows during the winter.

Some remarks about the structure of the earth-worm now appear apropos. Its body consists of from one hundred to two hundred almost cylindrical rings, each provided with minute bristles. The muscular system is well developed, thus enabling these animals to crawl backwards as well as forwards, and to retreat by the help of their affixed tails into their burrows with extraordinary rapidity. Situated at the anterior end of the body is the mouth. It is furnished with a little projection, variously called the lobe or lip, which is used for prehension. Behind the mouth, internally located, is a strong pharynx, which is pushed forwards when the animal eats, corresponding, it is said, with the protrudable trunk of other Annelids. The pharynx conducts to the œsophagus, on each side of the lower part of which are placed three pairs of large glands, called calciferous glands, whose function is the secretion of carbonate of lime. These glands are very remarkable organs, and their like is not to be found in any other animal. Their use is connected in some way with the process of digestion. The œsophagus, in most of the species, is enlarged into a crop in front of the gizzard. This latter organ is lined with a smooth, thick chitinous membrane, and is surrounded by weak, longitudinal, but powerful transverse muscles, whose energetic action is most effectual in the trituration of the food, for these worms possess no jaws, or teeth of any kind. Grains of sand and small stones, from the one-twentieth to the one-tenth of an inch in size, are found in their gizzards and intestines, and these little stones, independently of those swallowed while excavating their burrows, most probably serve, like millstones, to triturate their food. The gizzard opens into the intestine—a most remarkable structure, an intestine within an intestine—which runs in a straight line to the vent at the posterior end of the body. But this curious structure, as shown by Claparède, merely consists of a deep longitudinal involution of the walls of the intestine, by which means an extensive absorbent surface is secured.