Earth Worm (lumbricus terrestris, Linn.), an articulate animal belonging to the abranchiate division of the class of annelids. (See Annelida.) This well known worm has a long, cylindrical, contractile body, divided into many apparent rings (sometimes 150) by transverse wrinklings; the internal surface of the muscular envelope sends off annular septa, dividing the cavity of the body into as many chambers as there are segments, the partitions having openings which allow the passage of the contents of the general cavity from one chamber to the others. Each segment is provided with seto3 or bristles, beginning at the 14th ring from the head, four on each side, united in pairs, forming eight longitudinal rows, of which four are lateral and four inferior; they are short and rough, and are used as fulcra during creeping or climbing in the ground. The sense of touch is very acute, as is shown by the quickness with which they retire into the ground when touched, or at the jar produced by an approaching footstep; the sense is believed to be most acute toward the head, especially in the first segment. The eyes are wanting.
The mouth is near the anterior extremity of the body, without teeth, with two somewhat prominent lips; the pharynx is simple, short, and muscular, the oesophagus narrow, the stomach very muscular, and the intestine short, straight, constricted by the muscular septa, and opening at the posterior extremity of the body. The blood is red, and the circulation is complete and closed; the several pairs of simple, transverse canals, situated above the stomach, whose pulsations may be distinctly seen, may be considered the heart. The dorsal vessel lies upon the intestinal canal enveloped in the hepatic tissue. The blood, though red, is quite different from that of the vertebrates; according to Siebold, it contains colorless, spherical, unequal-sized granular globules; these, Quatrefages says, are not part of the blood, but belong to the fluid of the general cavity; the latter maintains that the coloring matter is in simple solution. There is no apparent external organ of respiration, and the peculiar canals in the abdominal cavity are regarded by some as internal branchiae or aquiferous vessels.
The structure of these organs is little understood; but in all genera of the division there are at the commencement of the intestine very tortuous canals, opening generally on the ventral surface; these canals are lined with ciliae, which have an undulatory movement always in one direction; they never contain air, according to Siebold, but circulate an aqueous respiratory fluid by means of the ciliae; even the terrestrial earth worms can live only in damp earth, from which they obtain the necessary aqueous fluid. In the lumbricus these canals are surrounded by a distinct vascular network; they appear to end in loops, and their external orifices have not been satisfactorily ascertained. The most probable opinion is that the respiration is carried on principally by the general integument, and partly by the vascular system on the walls of the intestine; the ciliated canals described by Siebold are believed by Quatrefages to be organs for the secretion of the mucus which invests the body; but Dr. Williams, in his "Report on the British Annelida" (1851), considers them as utero-ovaria. The lumbrici reproduce by sexual organs; their eggs are spherical and present nothing remarkable; the sexes are united in the same individual.
During the breeding season, from six to nine of the segments (from the 26th to the 37th, as generally described) are developed into a kind of collar, nearly surrounding the body, by which these animals seize each other during coition; its component glandular follicles secrete a whitish viscid fluid, probably used for the formation of their cocoons or egg cases. According to Dufour, these cocoons have a long narrow neck, each, in the largest species, containing from one to six eggs; the statement of Montegre that the young are born alive seems to be confirmed by the observations of Dr. Williams, who says that they escape from the egg before leaving the body of the parent. It seems certain from the experiments of Dufour (Annates des sciences na-turelles, t. v. p. 17, and t. xiv. p. 216, 1st series) that the earth worm reproduces by means of eggs; he describes them as an inch in length, of a corneo-membraneous consistence, deposited in the earth at a depth of from 6 in. to 6 ft., in localities where the soil is neither inundated nor too dry, isolated, and each egg containing one or two young.
Earth worms live in moist earth, in which they make galleries in all directions, swallowing the earth as they proceed; their food is principally soft and decaying vegetables, as may be proved by any one who chooses to watch a garden walk by the light of a lantern on a damp evening, when they may be seen creeping out of their holes, elongating their first tactile segment, feeling in all directions for food, and, seizing upon any suitable substance that presents itself with their projected proboscis, retiring backward into the ground; their constant presence in situations where there is decaying vegetable matter proves that their food is principally derived from such substances; they also, as Montegre observed, feed on animal matters; it seems more reasonable to believe, with De Blainville, that they swallow earth for the purpose of making progress in their galleries, than that they do this to extract humus or any other nutritious substance from it. They seek each other chiefly at night and in the latter part of spring, though some species have been noticed together at all times of the day, and during all the warm months; it is well known that they are most abundant on the surface of the ground during and after nocturnal rains.
It has long been believed that this animal possesses a remarkable power of reproducing parts lost by accident or design, even to the extent of forming perfect individuals from separated portions; the experiments of Duges prove that very important parts may be reproduced, and it may easily be believed that in a worm divided into two, the anterior portion might produce an anus by the simple contraction of the wound; but that the posterior portion should be able to reproduce cerebral ganglia, mouth, stomach, cardiac and sexual organs, cannot be admitted; the anterior may survive a long time, but the posterior division gradually dries up and dies. - Though occasionally marring the beauty of the garden walks by little hillocks of earth, they not only do not injure vegetation, but are useful in permitting air and water to penetrate the ground through the channels which they pierce in every direction, manuring the fields, and throwing up fine dirt around the roots of grass; a field in which no worms exist can be safely put down as of little value to the agriculturist; they are most active in spring, when most needed, and retire during winter deep into the ground; according to Mr. Darwin, they perform under ground that which the plough and the spade do on the surface, and have covered a field manured with marl, in the course of 80 years, with a bed of earth 13 inches thick.
Worms also furnish food for birds, moles, frogs, and other small animals, and are used as bait for many kinds of fish. The rapid ascent and descent of worms in the ground are easily understood from the action of their numerous setae; they have often been seen high up on perpendicular surfaces, and in situations which they could not have reached without climbing perpendicularly. In their movements they display great muscular force, each seta being moved by its appropriate system of muscles, and being capable of penetrating a deal board; in ascending perpendicular surfaces of glass or other impenetrable material, they must retain their hold by means of the tenacious mucus with which their skin is covered. - There is no question that many species have been confounded under L. terrestris (Linn.). The largest European species is called L. gigas, and is 18 in. long, and as large as the little finger; other common and smaller species are L. anatomicus and L. trapezoides. Whether all the American species are distinct has not been sufficiently demonstrated.
Those who wish to pursue this subject into its details are referred to the writings of Dufour, Duges, Milne-Edwards, Blanchard, and especially Qua-trefages in the Annales des sciences naturelles since 1828; to the article "Annelids," in the "Cyclopaedia of Anatomy and Physiology;" to the report of Dr. Williams, above quoted; and to Siebold's " Comparative Anatomy."
Earth Worm (Lumbricus terrestris).