370 



EmtsJurn of Natural fe 



other species see Mr. Gould's Birds of Aus- 

 tralia. 



LEAF-CUTTING BEES. [See MEGA- 

 CHILE.] 



LEECH. (Hirudo.) A genus of suctorial 

 animals, or red-blooded worms, of aquatic 

 habits, provided with a sucker at both ends 

 of the body : the greater part are inhabit- 

 ants of fresh water ; some, however, are 

 only found in the sea ; while others live in 

 moist situations near stagnant water, pur- 

 suing earth-worms, &c. Many of them accu- 

 mulate their eggs into cocoons, enveloped by 

 a fibrous excretion, at first sight so closely re- 

 sembling sponge in structure as to have been 

 once mistaken by a distinguished naturalist 

 for a new genus of that family. The species 

 which principally deserves our attention is 



f 



:is.) 



the common Leech (the Ilinido medicinalis 

 of Linnaeus). This species, which is usually 

 about the length of the middle finger, bears 

 a considerable resemblance to the earth- 

 worm in its general structure, but differs as 

 to the conformation of its mouth and di- 

 gestive apparatus. Its skin is composed of 

 from ninety to a hundred or more soft rings, 

 by means of which it acquires its agility, 

 and swims in the water. It has a small 

 head ; a black skin, edged with a yellow 

 line on each side, and some yellowish spots 

 on the back ; and the belty, which is of a 

 reddish colour, is marked with pale yellow 

 spots. But the most remarkable part is the 

 moutli, which is situated in the middle of 

 the cavity of the anterior sucker ; and three 

 little cartilaginous bodies, or jaws, are seen 

 to be disposed around it, in such a manner 

 that the three edges form three radii of a 

 circle. Each of these has two rows of mi- 

 nute teeth at its edge, so that it resembles a 



small semicircular saw. It is imbedded at 

 its base in a bed of muscle, by the action of 

 which it is worked, in such a manner as to 

 cut into the skin, a sawing movement 

 being given to each piece separately. It is 

 in this manner that the tri-radiate form of 

 the leech-bite is occasioned ; each ray being 

 a separate little saw, this apparatus enabling 

 the leech to penetrate the skin without 

 causing a dangerous wound. The lacerated 

 character of the wound is very favourable to 

 the flow of blood ; wliich is further promoted 

 by the vacuum created by the action of the 

 sucker. The alimentary canal consists of 

 an oesophagus, a long stomach, with ccecal 

 sacs, and an intestine. The operation of 

 digestion is extremely slow, notwithstanding 

 the rapid and excessive manner in which 

 the Leech fills its stomach ; a single meal 

 of blood will suffice for many months ; nay, 

 more than a year will sometimes elapse, 

 before the blood has passed through the ali- 

 mentary canal in the ordinary manner, 

 during all which period so much of the 

 blood as remains undigested in the stomach 

 continues in a fluid state. This accounts 

 for the reluctance of the Leech, after being 

 used to abstract blood, to repeat the opera- 

 tion ; it not only being gorged at the time, 

 but provided with a sufficient supply for so 

 much longer. Indeed, the true medicinal 

 Leech does not seem to take any solid ali- 

 ment, but subsists on the fluids of frogs, fish, 

 &c. Leeches are furnished with eight or 

 ten simple eyes, which may be detected 

 with a magnifying glass as a semi-circular 

 row of black points, situated above the 

 mouth upon the sucking surface of the oral 

 disc ; and to these visual specks it is sup- 

 posed they are indebted for whatever sight 

 they possess. 



Leeches derive their principal interest 

 from the use that is made of them as a re- 

 medial agent ; but it should be observed 

 that there are only two species so employed, 

 and these are principally derived from the 

 South of France, Sweden, Poland, and 

 Hungary. It is common for the leech- . 

 dealers to drive horses and cows into the 

 ponds, that the Leeches may fatten and pro- 

 pagate more abundantly by sucking their 

 blood. Children are also employed to catch 

 them by the hand ; and grown persons wade 

 into the shallow waters in the spring of the 

 year, and catch the Leeches that adhere to 

 their naked legs. In summer, when they 

 have retired to deeper waters, a sort of raft 

 is constructed of twigs and rushes, by which 

 a few are entangled. They are also taken 

 by laying baits of liver, to which the Leeches 

 resort, and are then caught ; but this last 

 method is thought to make them sickly. A 

 Leech may be known to be in good health 

 if it be active in the water, and plump when 

 taken out. The most certain method of 

 nducing Leeches to bite, is to cleanse the 

 skin thoroughly ; and they should be ex- 

 posed to the air for a short time previous to 

 their application, as by this means they will 

 bite more freely. If they are voracious, they 

 may be applied to the part by being held 

 lightly in the fingers, or they may be placed 

 in a leech-glass, which is a preferable mode. 



