The New Student's Reference Work/Earthworm

Earthworm, the common angleworm that burrows in the earth. The surface of the body is provided with small bristles which aid in crawling and in burrowing. The body is divided by furrows into a number of rings; those in front are larger than those in the middle and those behind are flatter, so that one can easily tell the head-end and the tail-end. The earthworm, although to general appearances so low in the scale of life, is wonderfully constructed, and is provided with organs of digestion, circulation, nervous life, etc. The digestive system is a muscular tube running through the body, having a crop and gizzard in its course; the front end of it is capable of being thrown out and drawn by a set of muscles. The food consists of animal and vegetable matter mixed with the soil, for example, minute fragments of old leaves, etc. Therefore the earthworm fills its alimentary tube with earth in which are scattered particles of animal and vegetable matter. The food is digested and absorbed into the system and the earth is voided again. In this way these worms work the soil over, and their influence is greater than one would at first suspect. Darwin showed that in an acre of garden, on an average, as much as fifteen tons of soil would pass through their bodies in a year. They also bring vegetable mould to the surface, and bury objects thrown upon the ground, at the rate of two inches or more in ten years. They have been important agents in burying ancient cities, temples, columns, coins, etc. They also are very beneficial to the soil in loosening it and working it over. They have a set of coiled tubes, a pair in each joint, except the first three or four, that remove from the body the worn-out material, and correspond to the kidneys of higher animals. These organs are characteristic of worms. The nervous system consists of a mass of gray nervous matter in the head, united by strands around the throat to a long cord of nervous matter running along the under surface of the body. The nerve-trunks are connected with this central cord, those of the head-end uniting with the brain, those from the rest of the body with the ventral cord. The earthworms have no eyes, but the entire fore end of the body is sensitive to light. They feed mostly at night, crawling from their burrows, and their places may be discovered by tubular castings of earth. There are many other worms composed, like the earthworms, of a series of rings. It is probable that the parentage of vertebrated animals was from simple animals somewhat like these ringed worms. No one thinks that the worms of to-day represent the ancestors of vertebrates, but it is generally believed by naturalists that the vertebrated animal came from very simple forms many thousand or million years ago, and those early remote parents were probably in structure somewhat like the living ringed worms. See Darwin: Formation of Vegetable Mould.