ARTICULATA. 97 
A species of leech finds its way under the eyelids, and into the nasal 
passages of Ardea virescens, in Martinique. In Algeria, Hamopis vorax is 
abundant, and attacks man and animals upon land; and it is found 
sticking to the inside of the mouth and throat of slaughtered cattle in that 
country. According to Baron Larrey, the French soldiers were much 
plagued by a small species which attached itself to the entrance of the 
throat. The same species was found in the nasal passages of the horse. 
As it is difficult for a leech to affix itself to an animal, except at rare 
intervals, it has been provided with peculiar digestive organs to enable it to 
undergo a long fast. The stomach is formed of a number of cells, each of 
which has a lateral sac upon each side. The entrance from the stomach 
to the intestine has a valve, and at the posterior extremity, of the intestine 
there is a sphincter to close it, so that the food may be admitted and 
retained in small portions as it is required, and it is a remarkable fact, that 
the blood thus kept in store (which may amount to nearly half an ounce) 
retains its natural properties for many months. Hence the difficulty of 
employing leeches in medicine when they have been gorged within some 
months. This difficulty is obviated in some degree, by forcing them to 
disgorge a part of the blood. by pressure, and a mode has been discovered 
by piercing them with a lancet one third the length from the head, and 
placing them in tepid water, when the contents of the stomach will escape, 
especially if assisted by pressure. The wound heals in a few days, and the 
leech may be applied again in fifteen or eighteen days. 
These animals are monoicous and oviparous, the eggs being deposited in 
a kind of cocoon, resembling in size and form that of the silkworm, its 
material resembling fine sponge. A Swedish species deposits its eggs in 
the earth at some distance from the water. 
Among the genera are Hirudo (Z. officinalis, pl. TT, fig. 26), Malaco- 
bdella (M. grossa, fig. 22), referred to in page 43; Clepsina (fig. 24), 
Hemopis (H. vorax, jig. 25). Two species of leech are almost exclusively 
used in medicine: Hvrudo officunalis, the green or Hungarian leech, the 
belly of which is without spots; and A. medicinalis, the German or brown 
leech, with a spotted belly. 
The mouth of those leeches which are capable of biting, is tri-radiated, 
each ray having a tooth which resembles a segment of a minute circular 
saw, the margin of which is armed with a double row of microscopic 
denticulations. The suction, whilst it draws the skin within the reach of 
the teeth, renders it tense, so that they act like lancets, and the apparatus 
answers the double purpose of a small scarificator and cupping-glass. An 
examination of the wound made by a leech will show the tri-radiated 
arrangement of the teeth. Artificial leeches are sometimes made use of, 
the quality of which must greatly depend upon the accuracy with which 
the natural instrument is imitated. 
Three species of Hirudo, and one of Clepsina, have been described from 
the waters of the United States. 
It was at one time believed that changes in the weather might be 
foretold from the actions of leeches, but the value of these indications was 
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