468 



HISTORY OF INSECTS. 



mer, undergoes no varieties of transformation ; 

 but when once excluded from the body of the 

 parent, preserves its first figure to the end. I 

 place the history of the Leech among the first 

 class of insects ; while I have degraded the 

 earth-worm, the Tasnia, and the Polypus, into 

 the class of zoophytes, or that imperfect tribe 

 which serves to make the shade between ani- 

 mal and vegetable nature. Not but that the 

 earth-worm or the polypus have their motions, 

 their appetites, and their vital principles, as 

 complete as the leech, and, to a cursory view, 

 appear every way as complete animals. But 

 there is one circumstance that lays the line 

 between them; that exalts the one, and de- 

 grades the other. The earth-worm and the 

 polypus may be cut into pieces, and each piece 

 will produce a new and perfect animal : the 

 leech cannot suffer this dissection, but dies 

 when cut in two ; an evident instance that it 

 is possessed of a more perfect organization 

 than those animals which it otherwise very 

 much resembles. 



The leech, from its uses in medicine, is one 

 of those insects that man has taken care to 

 provide ; but, of a great variety, one kind only 

 is considered as serviceable. The horse-leech, 

 which is the largest of all, and grows to four 

 inches in length, with a glossy black surface, 

 is of no use, as it will not stick to the skin ; 

 ihe snail-leech is but an inch in length ; and 

 though it will stick, is not large enough to ex- 

 tract a sufficient quantity of blood from the pa- 

 tient; the broad-tailed leech, which grows to 

 an inch and a half in length, with the back 

 raised into a sort of ridge, will stick but on 

 very few occasions : it is the large brown 

 leech, with a whitish belly, that is made use 

 of in medicine, and whose history best merits 

 our curiosity. 



The leech has the general figure of a worm, 

 and is about as long as one's middle finger. 

 Its skin is composed of rings, by means of 

 which it is possessed of its agility, and swims 

 in water. It contracts itself, when out of 

 water, in such a manner, that when touched it 

 is not above an inch long. It has a small 

 head, and a black skin, edged with a yellow 

 line on each side, with some yellowish spots 

 on the back. The belly also, which is of a 

 reddish colour, is marked with whitish yellow 



gatherers as a favourable time for collecting them. The 

 property by which a leech anticipates thunder, has in- 

 duced some persons to employ it as a species of barom- 

 eter; but its indications are very uncertain. 



The Horse-Leech, (Hirudo sanguisuga), is much 

 larger than the medicinal leech, and altogether of a 

 greenish black. It is said to be dangerous, from the 

 wounds which it inflicts ; but much difference of opinion 

 exists, even among learned naturalists, as to its power of 

 drawing blood. 



Leeches prey on worms, tadpoles, &c., which they 

 devour with avidity. 



spots. But the most remarkable part of this 

 animal is the mouth, which is composed of 

 two lips, that take whatever form the insect 

 finds convenient. When at rest, the opening 

 is usually triangular ; and within it are placed 

 three very sharp teeth, capable of piercing not 

 only the human skin, but also that of a horse 

 or an ox. Still deeper in the head is disco- 

 vered the tongue, which is composed of a strong 

 fleshy substance, and which serves to assist 

 the animal in sucking, when it has inflicted 

 its triple wound ; for no sooner is this vora- 

 cious creature applied to the skin, than it 

 buries its teeth therein, then closes its lips 

 round the wounds which it has made ; and 

 thus, in the manner of a cupping-glass, 

 extracts the blood as it flows to the different 

 orifices. 



In examining this animal's form farther to- 

 wards the tail, it is seen to have a gullet and 

 an intestinal canal, into which the blood flows 

 in great abundance. On each side of this are 

 seen running along several little bladders, 

 which, when the animal is empty, seem to be 

 filled with nothing but water ; but when it is 

 gorging blood, they seem to communicate with 

 the intestines, and receive a large portion of 

 the blood which flows into the body. If these 

 bladders should be considered as so many sto- 

 machs, then every leech will be found to have 

 twenty-four. But what is most extraordinary 

 of all in this animal's formation is, that though 

 it takes so large a quantity of food, it has no 

 anus or passage to eject it from the body when 

 it has been digested. On the contrary, the 

 blood which the leech has thus sucked remains 

 for several months clotted within its body, 

 blackened a little by the change, but no way 

 putrified, and very little altered in its texture 

 or consistence. In what manner it passes 

 through the animal's body, or how it contri- 

 butes to its nourishment, is not easily accoun- 

 ted for. The water in which they are kept is 

 very little discoloured by their continuance ; 

 they cannot be supposed to return the blood by 

 the same passage through which it was taken 

 in : it only remains, therefore, that it goes off 

 through the pores of the body, and that these 

 are sufficiently large to permit its exclusion. 



But it is not in this instance alone that the 

 leech differs from all other insects. It was 

 remarked in a former chapter, that the whole 

 insect tribe had the opening into their lungs 

 placed in their sides, and that they breathed 

 through those apertures as other animals 

 through the mouth. A drop of oil poured on 

 the sides of a wasp, a bee, or a worm, would 

 quickly suffocate them, by stopping up the 

 passages through which they breathe : but it 

 is otherwise with the leech, for this animal 

 may be immersed in oil without injury ; nay, 

 it will live therein ; and the only damage it 



