370 EARTHS EARTH WORM is kept in a state to follow down after the shrinking nucleus; little by little they accom- plish in each locality a work that would other- wise be accomplished by sudden and terrible paroxysms overspreading the whole earth. Earthquake-proof Buildings. The views of Mallet as to the nature of the movement of the surface of the earth during an earthquake shock have enabled him to define certain prin- ciples according to which buildings may be constructed so that they shall be able to resist any shock that is likely to visit them. These principles have been already applied by Mallet and Stevenson in the construction of light- houses for the Japanese government, and by Mr. W. Lloyd in the construction of the new custom house at Valparaiso. EARTHS, the oxides of the metals aluminum, glucinum, thorinum, zirconium, lanthanum, er- bium, and yttrium, called alumina, glucina, &c. They are often called the earths proper, to distinguish them from the alkaline earths, baryta, strontia, lime, and magnesia, the oxides of the metals barium, strontium, calcium, and magnesium. Before the decomposition of some of them by Sir Humphry Davy they were thought to be elements. Silica was for- merly regarded as an earth; but on account of its forming definite compounds with the earths in which they act the part of bases, it must be classed as an acid. The earths gen- erally exist in nature in combination with silica ; although in the varieties of corundum, such as the gems sapphire, ruby, oriental to- paz, and oriental amethyst, alumina exists principally as oxide, the Indian sapphire hav- ing the composition A^Os, 97'5 per cent. ; magnesia, T9 ; silica, '8 per cent.; and the Indian ruby containing barely more than 1 per cent, of silica. In feldspar alumina is found combined with silica, sometimes with silicate of soda, but more frequently with silicate of potash. The gem hyacinth is composed of silicate of zircon. The silicate of glucina is found in the beryl and erbium. Associated yttrium is found, combined with silica, in the mineral gadolinite. EARTH WORM (lumbricus terrestris, Linn.), an articulate animal belonging to the abranchi- ate 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 trans- verse wrinklings ; the internal surface of the muscular envelope sends off annular septa, di- viding 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 pro- vided with seta 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 in- ferior ; 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 an- terior extremity of the body, without teeth, with two somewhat prominent lips ; the phar- ynx is simple, short, and muscular, the oesoph- agus 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, sit- uated above the stomach, whose pulsations may be distinctly seen, may be considered the heart. The dorsal vessel lies upon the intes- tinal 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 respira- tion, and the peculiar canals in the abdominal Earth Worm (Lumbricus terrestris). cavity are regarded by some as internal bran- chiaB or aquiferous vessels. The structure of these organs is little understood; but in all genera of the division there are at the com- mencement of the intestine very tortuous canals, opening generally on the ventral sur- face ; these canals are lined with cilire, 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 cilise ; even the terres- trial earth worms can live only in damp earth, from which they obtain the necessary aqueous fluid. In the lumbricus these canals are sur- rounded by a distinct vascular network ; they appear to end in loops, and their external ori- fices have not been satisfactorily ascertained. The most probable opinion is that the respira- tion 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 Anne- lida" (1851), considers them as utero-ovaria. The lumbrici reproduce by sexual organs ; their eggs are spherical and present nothing
