LEECHES, highly specialized Amielida constituting the order Hirudinea or Di.rcophora. They are distinguished from most other anne lids by the nearly complete Obliteration of the axiom or body-cavity, owing to the develop went of parenchymatous connective tissue, muscles, etc., the presence of an anterior or oral sucker and a posterior or subanal sucker, and by the absence of setw., except in Acan thobdella. In all leeches which have been care fully studied there are exactly 34 segments or somites, each represented by a ganglion in the central nervous system, and being of smaller size and simpler structure toward the ends than in the middle of the body, where each is divided into from 2 to 12 rings, one of which, sometimes regarded as the first, sometimes as the middle ring, bears metameric, eye-like sense organs. Most leeches are temporary parasites, a few nearly permanent parasites; the rest are predatory hunters or scavengers, or they may change from one mode of life m another. They are marine, fresh-water or. terrestrial. The first class is most abundant, both in indi viduals and species, in cold seas, the second is both temperate and tropical and the third is confined to warm regions. Four families are distinguished: the Ichthyobdellidep or fish leeches, the Glossiphonidie or tortoise and snail leeches, the Herpobdellidce or worm-leeches and the or jawed leeches. The first two families possess a long protrusible pro boscis and are much more closely allied than the Herpobdellidce and Hirudinidce, which have no proboscis, The Ichthyobdellida• are chiefly parasitic on fishes and, except a few-fresh •ater forms, are marine. Some of them, as Branchellion, are branchiate. The Glossi
phonidce are' richly represented in the fresh 'water lakes and streams of North America a great variety of species, most of which' attach themselves to tortoises, whose blood they suck, or else' they devour water-snails and small worms. A few are parasitic on fishes. In all of them' the oral sucker is small and the eyes in one to four pairs placed near the median line. The Herpobdellidre contains slender, 'six or eight-eyed, predaceous leeches, which are extremely abundant in fresh-water ponds •and feed on small leeches and worms. no toothed jaws and the digestive tract is simple and straight. The Hirudinidce have 10 eyes, generally three-toothed jaws and a spacious sacculated digestive tract. Here belong the true blood-sucking leeches, the medicinal• leech of Europe and our native Macrobdella decora, also formerly largely employed in this country for blood-letting. The only terrestrial leech of the United States belongs to this family. It inhabits garden soil, feeds on earthworms and is one of the largest leeches known. Consult Beddard, F. E., 'Earthworms and Leeches' (in 'Cambridge Natural History,' Vol. IT, Cambridge 1901); id., 'Earthworms and their Allies) (New York 1912) ; Leuckart and Brandes, des Menschen); Moore, J. 'The Leeches of the United States National (in 'Proceedings' of the United States National Museum, Vol. XXI, Washington 1899); Verrill, A. E., 'Invertebrate Animals of Vineyard Sound' (ib. 1874) ; Whitman, Quar terly Journal Microscopical Science (1886) •, Moore, 'Bulletin Illinois State. Laboratory of Natural History' (1901).