LEECH (AS. /wee, leech, physician. Goth. kkei.%, (111G. lahhi. Mehl, physician. from AS. hie, medicine. gift). An annelid of the order or class Hirudinea, divided into a number of gvoups. Ilirudinith•, etc., some of which contain many species. They are mostly inhabitants of fresh waters, although some live in grass, etc., in moist places. and some are marine. They are most common in warm climates. The body is soft and eompi•sed of segments (e.g. Pontof NH la i like that of the earth-worm, but not fur nished with bristles, except in one genus, to aid in as in the earth-worm; instead of which. a sucking-disk at each extremity enables the leech to avail itself of its power of elongating and shortening its body, by means of which it moves with considerable rapidity. The external rings (annuli) which show in the body-wall do not correspond to the inner segments. lout are much inure numerous. While there are usually 33 segments. the number of rings may lie more than 200. There are, at the middle of the body, 3, 5, G. or 12 rings to each segment. The month is in the anterior sueking-di-k. The month of many of the species is admirably adapted not only for killing and eating the minute aquatie animals which constitute their ordinary food, but for making little wounds in the higher ani mals, through which blood may he sueked. The mouth of the medicinal leech has three small. white, hard pharyngeal teeth, minutely serrated along the edges. and curved so as to fi rm little semicircular saws. provided with muscles power ful enough to work them with great effect. and to produce a triradiate wound. i.e. three short. deep gashes. radiating from a common centre, whence some of the rather fanciful names. such as drag on-leech. The stomach is very large, and is di vided into eompartmcnts, some of which have large lateral efeen: and a leech which has once gorged itself with blood retains a store for a very long time, little changed, in these receptacles. while the digestive process goes slowly on. The circulatory system consists of four great pulsat ing trunks—one dorsal, one ventral, and two lat eral—with their branches; there is no heart. The blood system is in such close and intimate re• lotion with the body-cavity that it is difficult to determine accurately the limits of each. The tion of the blood takes place in the skin. or rarely by special outgrowths of the body-walls, which function as gills. Leeches are oviparous, and each individual is hermaphroditic, while in certain allied forms etc.) the sexes are distinct. The eggs are laid in sacs, or. as in Clepsine, the tish-leech. are covered with a transparent fluid substance which hardens and envelops the eggs. is usually. direct,
and there is 110 metamorphosis, the young being like the adult. \\lien feeding the leeches pair and one impregnates the other by passing sper matophores through the penis into the vagina. :simultaneous mutu 1 fertilization has also been described. They have small eves (in the medici nal leech ten). which appear as black spots ou the dorsal side of the segment, back of the mouth. These eves are very simple and seem to be merely od fied sense-papilla.. of which there are many arranged in longitudinal rows, the whole length of the body. Leeches vary much in size and color. Some species are less than half an inch long, while Jlaerolidella •ahlrianu is said to reach a length of Iwo and a half feet. Sonic are very slender, while others are broad and very flat. The colors are usually dull gray, brown, dark green, and black.
Leeches frequently change their skin; and one cause of the great mortality so often experienced among leeches kept for medicinal use is the want of aquatic plants in the vessels containing them, among which to rub themselves for aid in this process, and for getting quit of the slime which their skins exude. Leech aquaria in which aqua tic plants grow- are, therefore, inneh more favor able for the health of leeches than the tanks and vessels formerly in use. The medicinal leech (Thrudo medieinalis) is a European species, a rare native of Great Britain: leeches, however, are generally imported from Hamburg and from the south of Europe. The ancients were well ac quainted with leeches, but their medicinal use seems to have originated in the Middle Ages. The horsedeech ( Mcnropis &anynisorba) is coin MOil in Great it is mulch larger than the medi cinal species. hut its teeth are comparatively blunt, and it is little of a blood-sucker, and useless for medicinal purposes. In ninny parts of India, as in the warm valleys of the Him alaya, the moist grass swarms with leeches. some of them very small. but very trouble some to cattle and men who have occasion to walk through the grass. The moist valleys of Java. Sumatra, Chile. and other tropical countries swarm with land-leeches. Many species of leech are found in the 'United States, the neon ones belonging to the genera Nephelis and Glossiphonia (better known as Clepsine). For a of the North American species. con sult: 'Verrill. Invertebrate Animals of Vineyard ,c:oand (Washington. IS74) ; Moore. "The Leeches of the United States National Museum;' in Proreed;ngs of the United States National Mu scum. vol. xxi. (Washington, 1593).