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LEECH

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Originally appearing in Volume V16, Page 366 of the 1911 Encyclopedia Britannica.
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LEECH , the See also:

common name of members of the Hirudinea, a See also:division of Chaetopod See also:worms. It is doubtful whether the medicinal leech, Hirudo medicinalis, which is rarer in See also:England than on the See also:continent of See also:Europe, or the See also:horse leech, Aulastoma gulo, often confused with it, has the best right to the See also:original See also:possession of this name. But at See also:present the word " leech " is applied to every member of the See also:group Hirudinea, for the See also:general structure and See also:classification of which see See also:CHAETOPODA. There are many genera and See also:species of leeches, the exact See also:definitions of which are still in need of a more See also:complete survey. They occur in all parts of the See also:world and are mostly aquatic, though sometimes terrestrial, in See also:habit. The aquatic forms frequent streams, ponds and marshes, and the See also:sea. The members of this group are always carnivorous or parasitic, and See also:prey upon both vertebrates and invertebrates. In relation to their parasitic habit one or two suckers are always See also:developed, the one at the anterior and the other at the posterior end of the See also:body. In one subdivision of the leeches, the Gnathobdellidae, the mouth has three chitinous jaws which produce a triangular bite, though the See also:action has been described as like that of a circular saw. Leeches without biting jaws possess a protrusible See also:proboscis, and generally engulf their prey, as does the horse leech when it attacks earthworms. But some of them are also ectoparasites. The leech has been used in See also:medicine from remote antiquity as a moderate See also:blood-See also:letter; and it is still so used, though more rarely than formerly.

As unlicensed blood-letters, certain See also:

land-leeches are among the most unpleasant of parasites that can be encountered in a tropical See also:jungle. A species of Haemadipsa of See also:Ceylon attaches itself to the passer-by and draws blood with so little irritation that the sufferer is said to be aware of its presence only by the trickling from the wounds produced. Small leeches taken into the mouth with drinking-See also:water may give rise to serious symptoms by attaching themselves to the See also:fauces and neighbouring parts and thence sucking blood. The effects of these parasites have been mistaken for those of disease All leeches are very extensile and can See also:contract the body to a plump, See also:pear-shaped See also:form, or extend it to a See also:long and See also:worm-like shape. They frequently progress after the See also:fashion of a " looper " See also:caterpillar, attaching themselves alternately by the anterior and the posterior sucker. Others swim with See also:eel-like curves through the water, while one land-leech, at any See also:rate, moves in a gliding way like a land Planarian, and leaves, also like the Planarian, a slimy trail behind it. Leeches are usually See also:olive See also:green to See also:brown in See also:colour, darker patches and spots being scattered over a paler ground. The marine parasitic leech Pontobdella is of a See also:bright green, as is also the land-leech Trocheta. The See also:term " leech," as an old See also:English synonym for physician, is from a See also:Teutonic See also:root meaning " heal," and is etymologically distinct from the name (O. Eng. lyce) of the Hirudo, though the use of the one by the other has helped to assimilate the two words. (F. E.

End of Article: LEECH

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