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THE MEDICINAL LEECH-HORSE LEECH.
THE MEDICINAL LEECH, AND HORSE-LEECII.
This species of Leech is of an olive black color, with six yellowish lines above, and spotted with yellow beneath. It is generally two or three inches in length.
In stagnant ponds and ditches these animals are most commonly found. Their body is formed with numerous annular wrinkles, which they have the power of expanding or contracting at pleasure. The til ends in a circular muscle or sucker, which, when applied to any substance, readily adheres, by the animals drawing up the middle, so as to have it pressed firinly down by the external air. By this it fastens itself with ease and security, while it extends the other part of its body in any direction; and it is so firmly fixed, that it can move its head about to seek for nourishment, without any danger of being carried away by the strength of the current. When the Leech is desirous of moving onward, it extends its body, fixes its head in the same manner that it did its tail; then loosens and draws that up; and again fastens it near its head, as a fresh point to proceed from.
The head of the Leech is armed with three teeth, of a slightly car. tilaginous substance, which are so situated as to converge when the animal bites, and leave a somewhat triangular mark on the skin. These teeth are sufficiently strong to pierce the skin of an ox or a horse. Through the holes it forms with them, it sucks the blood; this is done by contracting the muscles of the throat, so as to make the blood rush through the vacuum above the wound into the stomach, a kind of membranaceous receptacle, divided into twenty four small cells. Here the blood remains, sometimes for months, and affords support to the animal during the whole time. It passes off by transpiration, the matter fixing on the surface of the body, and afterwards coming off in small threads. In proof of this, if a Leech be immersed in oil, (where it may be kept alive for several days,) and afterward put into water, a kind of slough will be seen to loosen from its skin, exactly of the shape of the body.
It is stated, that a large-sized Leech will generally draw about an ounce of blood. These animals will sometimes adhere so long, and become so much distended, as afterwards to die in consequence. They are, at any time, easily loosened from the skin, by putting upon them salt, pepper, or acids.
Horse-leeches are equally, if not more, abundant in ditches and stag. aant waters, than the former species. They are so greedy of blood, that a vulgar notion is prevalent, that nine of them are able to destroy a horse. Medical men, in general, are cautious not to use them, from an opinion, though probably a groundless one, that their hite is noxious.
OF THE SLUGS IN GENERAL,
THE Linnean order Mollusea consists of all those simple animals which are without shells, and are furnished with tentacula or arms. The greater number of them ere inhabitants of the sea.
Few animals, for their size, are more voracious than these. They would do serious injury to our fields and gardens, were not their numbers abridged by several of the smaller quadrupeds, and by various species of birds.
They have so strong a tendency to reproduction, that, if the head or tail be cut off, these parts will grow again. Most of the species can exist for a great length of time, even for several months successively, without food.
THE SMALL GRAY SLUG, AND BLACK SLUG.
In moist gardens, meadows, fields, and woods, the former of these
Slugs is but too common. Its We time of going abroad in search of
food is in the evening and night,
During the day it lies concealed, O either
either among the leaves of vegetables or under the surface of the ground.
Its progress on the ground may be easily traced by tbe slime which it leaves in its track. Few animals are more de. structive to vegetation than these.
These Slugs sometimes suspend themselves by a kind of thread, formed from the viscid substance which covers their bodies.
The Black Slug, or Snail, is a well-known inhabitant of our fields and meadows, during the summer season. The country people consider the appearance of this Slug as an indication of approaching rain; but this is rather to be accounted for by the moisture of the ground and of the plants. It is seldom indeed to be observed abroad during dry weather, for this would deprive the external parts of its body of the moisture which is requisite for its subsistence. The Black Slug feeds on the roots and leaves of different kinds of plants.
THE BLACE SLOO.
THE APLYSIA, AMPHITRITE AND NERES TRIBES.
OF THE APLYSIA TRIBE.
The species of Aplysia, are only three in number. One of them inhabits the European seas, another the shores of Barbary, and the third the coasts of America.
These animals respire water by means of branchiæ, which form a kind of tuft on the back, and which are covered with an operculum or lid.
OF THE AMPHITRITES.
THERE is no tribe of marine animals that exceed these in beauty. They inhabit tubes of a horny or tendinous substance, the greater part of which is buried in the sand, or mud, at the bottom of the sea. From the upper extremity of these tubes, they push out a great number of elegant tentacula, which are arranged about the mouth like rays from the centre of a circle.
The species are numerous; and several beautiful kinds have, of late years, been discovered to inhabit the English coasts.
OF THE NEREIS TRIBE.
THESE are all marine animals. They are very various in size; some are invisibly minute, and others are several inches in length. They have been denominated Marine Scolopendræ or Centipedes; and, in some respects, they bear a strong resemblance to these animals.
By numerous legs with which they are furnished, they are enabled to move about among submarine rocks and stones, with considerable agility. Under these they conceal themselves, and lie in ambush for their prey, which chiefly consists of minute worms of different kinds.
The Night-shining Nereis.— These minute creatures inhabit every sea; and are one of the causes of the luminous shining of the water in the night. They are found on all kinds of marine plants; but often leave them, and swim on the surface of the water. They are frequent at every season of the year, but particularly in summer, before stormy weather, when they become more agitated and more luminous than at at other times. So minute are they, that myriads of them may be contained in a small cup full of sea-water. Innumerable quantities of them lodge in the cavities of the scales of fishes; and to them, probably, the fish may, in some measure be indebted for their luminous quality.
OF THE ACTINIÆ, OR SEA ANEMONES.
These animals are of a somewhat oblong form, and, when closed, resemble a truncated cone. They are fixed by the base; and from the
THE COMMON, OR PURPLE SEA-ANEMONE.
upper part of their body occasionally extend several tentacula, which are disposed in regular circles. The mouth is situated at the top, in the centre of the tentacula, and is furnished with crooked teeth.
They are all capable of varying their figure; but, when their tentacula are fully expanded, they have the appearance of full-blown flowers. Many of them are of very beautiful and brilliant colors. They feed on shell-fish, and other marine animals, which they draw into their mouth by means of their arms; and they eject the shells and other indigestible parts through the same opening. It, however, sometimes happens, that a shell presents itself in a wrong position, and the animal is not able to discharge it in the usual manner: in this case, we are told that the shell is forced through the body, making a wound, as if with a knife, near the base. The arms of the Sea-anemones seem to lay hold of objects by making a vacuum ; for on touching them with the fingers, they readily adhere, but no viscous matter is deposited by them. The mouth of these animals is capable of great extension, so as to allow them, without injury, to swallow very large shells. The whole interior of their body is one cavity or stomach. They have the power of progressive motion : but this is extremely slow, and is said to be performed by loosing their base from the rock, reversing their body, and employing their
tentacula as legs. Nearly all the
animals of this tribe may be separated from the rocks by a card carefully introduced beneath, so as not materially to injure them; and, if put into glass vessels with sea-water, which must be changed about once a week, they will there fix themselves, and may be kept alive and in full vigor for a great length of time, even in places far distant from the sea-coasts.
All the species are viviparous.
THE COMMON, OR PURPLE SEA-ANEMONE.
On the submarine rocks of several of the European coasts, and on
those of the British is. lands in particular, these animals are extreme ly abundant. They adbere by their base so firmly to the rocks, ag frequently to be left above water at the ebbing of the sea : but they are generally found at a little depth below the surface. When closed, their form is that of a rounded cone, with an
orifice at the top. If kept in a vessel of salt-water, they will continue to live and flourish for a considerable length of time. It is
, however, remarkable
THE ROSE-COLORED SEA-ANEMONE.
when from want of the water being changed, they become unhealthy, they protrude their intestines at the mouth, and at length turn inside out, their mouth closing round the base. On renewing the water they will sometimes recover, and assume their natural shape and appearance.
THE ROSE-COLORED SEA-ANEMONE.
On this species the Abbé Dicquemaire made several experiments to ascertain its power of production, and other remark. able properties. He first cut off all the tentacula: these grew again in less than a month ; and, on repeating this apparently cruel operation a second and a third time, he had equal success. One of the animals had its upper part cut off: the base was found, a few days, afterward, to have fallen from its place, but it soon entirely recovered its limbs. After cutting one of these Anemones in two, the Abbé offered a piece of a muscle to the detached part, and the limbs seemed eager to take it. They drew it into the mouth, and it was swallowed; but, as the body was wanting to receive it, the piece came out at the opposite end; "just (says the Abbé) as a man's head, being cut off, would let out at the neck the bit taken in at the mouth." It was offered a second time, and again received and retained till the following day, when it was thrown up. In this manner it was fed for some time, the bits, when they did not pass through, appearing considerably altered on their re-appearance at the mouth. If the base of any of the Anemones happened to be injured by the incision, the wound generally proved mortal.
On being put under the receiver of an air-pump, and having the air exhausted, these animals did not seem to experience any ill-effects, nor to perceive any
difference between this and their being in the open air: if their tentacula happened to be expanded, they remained so, and not the least shrinking could be perceived.
These animals are destitute of eyes, yet they are very evidently affected by light. If a candle be held over the glasses in which they are kept, and at such a distance as not to communicate any heat, they regularly close, and do not again expand until the light is removed.
SECTION OF AXENONE
OF THE SEPIA, OR CUTTLE-FISH TRIBE.
The structure of these animals is very remarkable. Their body is cylindrical, and, in some of this species, entirely covered with a fleshy sheath; in others, the sheath reaches only to the middle of the body. They have eight tentacula or arms, and in general two feelers as they are called, which are much longer than the arms. Both the feelers