LEECH

This article appears in Volume V16, Page 366 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: LAP-LEO

LEECH , the common name of members of the Hirudinea, a division of Chaetopod worms. It is doubtful whether the medicinal leech, Hirudo medicinalis, which is rarer in England than on the continent of Europe, or the horse leech, Aulastoma gulo, often confused with it, has the best right to the

original

ORIGINAL

possession of this name. But at present the word " leech " is applied to every member of the group Hirudinea, for the general structure and classification of which see CHAETOPODA. There are many genera and species of leeches, the exact definitions of which are still in need of a more complete survey. They occur in all parts of the world and are mostly aquatic, though sometimes terrestrial, in habit. The aquatic forms frequent streams, ponds and marshes, and the sea. The members of this group are always
carnivorous or parasitic, and

prey

PREY (0. Fr. preie, mod. proie, Lat. praeda, booty, from prae and the root hed—seen in prehendere, prendere, to grasp)

upon both vertebrates and invertebrates. In relation to their parasitic habit one or two suckers are always developed, the one at the anterior and the other at the posterior end of the

body

BODY

. In one subdivision of the leeches, the Gnathobdellidae, the mouth has three chitinous jaws which produce a triangular bite, though the action has been described as like that of a circular saw. Leeches without biting jaws possess a protrusible proboscis, and generally engulf their

prey

PREY (0. Fr. preie, mod. proie, Lat. praeda, booty, from prae and the root hed—seen in prehendere, prendere, to grasp)

, as does the horse leech when it attacks earthworms. But some of them are also ectoparasites. The leech has been used in

medicine

MEDICINE

from remote antiquity as a moderate blood-

letter

LETTER (through Fr. lettre from Lat. littera or litera, letter of the alphabet; the origin of the Latin word is obscure; it has probably no connexion with the root of linere, to smear, i.e. with wax, for an inscription with a stilus)

; and it is still so used, though more rarely than formerly. As unlicensed blood-letters, certain land-leeches are among the most unpleasant of parasites that can be encountered in a tropical jungle. A species of Haemadipsa of 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-water may give rise to serious symptoms by attaching themselves to the 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

contract

the

body

BODY

to a plump, pear-shaped form, or extend it to a

long

LONG, GEORGE (1800-1879)
LONG, JOHN DAVIS (1838– )

and worm-like shape. They frequently progress after the fashion of a " looper "

caterpillar

CATERPILLAR

, attaching themselves alternately by the anterior and the posterior sucker. Others swim with eel-like curves through the water, while one land-leech, at any rate, moves in a gliding way like a land Planarian, and leaves, also like the Planarian, a slimy trail behind it. Leeches are usually olive green to brown in colour, darker patches and spots being scattered over a paler ground. The marine parasitic leech Pontobdella is of a

bright

BRIGHT, JOHN (1811-188g)
BRIGHT, SIR CHARLES TILSTON

green, as is also the land-leech Trocheta.
The

term

TERM

" leech," as an old English synonym for physician, is from a Teutonic 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. B.)

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