« AnteriorContinua »
lopes. They have red blood, and their circulation is by arteries and veins, but they have no special organ for the maintenance of the systole and diastole, their Creator not having given them a heart, but where the veins and the arteries meet, there is an enlargement, and the systole and diastole is more visible, as Cuvier remarks, than in the rest of the system, these enlargements therefore seem to represent a heart.
Savigny, in the third part of his Systême des Animaux sans Vertèbres divides them into five Orders, of which he gives only the characters of the four first, intending to publish, in a sup plement, his account of the fifth; these Orders he arranges in two Divisions-the first including those that have bristles for locomotion, and the second those that have them not.
1. His first Order he denominates Nereideans,' and characterizes them as having legs provided with retractile subulate bristles, without claws; a distinct head with eyes and antennæ; a proboscis that can be protruded, generally armed with maxillæ.
2. The second he names Serpuleans, these add to the legs of the former retractile bristles, with claws; they have no head furnished with eyes and antennæ, and no proboscis.
3. The third he names Lumbricinans; these have no projecting legs; but are furnished with bristles seldom retractile: they have no head with eyes and attennæ, and no maxillæ.
4. His fourth Order he names Hirudineans. They have a prehensile cavity, or sucker, at each extremity, and eyes.
5. In his fifth Order he intends to comprehend those Annelidans that have neither bristles nor prehensile cavities, but his account of this has not been published.
He begins with the most perfect of the Annelidans, but viewing them in connexion with the worms I must reverse the order, and instead of descending ascend, which will bring me ultimately into connexion with the more distinctly jointed animals the Condylopes.
1. The Order of Hirudineans includes animals that are of the first importance, as well as some that are fearfully anoying, to mankind. The common leech' has long been so much in request with medical men, on account of the facility with which it can be applied to any part of the body where bleeding is required, that they are now become scarce in our own waters, and consequently dear, so that large numbers are imported from the Continent.
2 Serpulex. 3 Lumbricinæ and Hirudines 4 Hirudo medicinalis, L. (Sanguisuga, Sav.);
Providence has gifted these animals with a sucker on the underside at each extremity of their body, by which their locomotions are performed, and by means of the anterior one they fix themselves to any animal that comes in their way. We see therefore in them, though on a larger scale, some approxima tion to the locomotive and prehensile organs of some of the Cephalopods, and prior to them, of the Stelleridans and Echinidans, which likewise move and fix themselves by suckers. The mouth is situated in the cavity of the oral sucker, it is triangular and armed with three sharp teeth disposed longitudinally in a triangle, two being lateral and one intermediate, and higher up. These teeth are sharp enough to pierce not only the human skin, but even the hide of an ox, and have their edge armed with two rows of very minute teeth: at the bottom of the mouth is the organ of suction which imbibes the blood flowing from the wound made by the teeth. These animals inhabit fresh waters, in which they swim like eels with a vermicular motion. In moving on a solid body, they first fix themselves by their anal sucker, which is larger than the oral, and then by means of their annular structure, extend themselves forwards, when they fix their mouth, detach their anal sucker, and thus fixing themselves alternately by each proceed with considerable rapidity. They are hermaphrodites, and bring forth their young alive. When in their native wa ters they suck any animal that comes in their way, even those with white blood, as the larvæ of insects, worms and the like.
Herodotus relates that the crocodile, in consequence of its frequenting the water so much, has the inside of its mouth in fested by leeches, which a little bird, named the trochilus, enters and devours, without receiving any injury from the monster. Geoffroy St. Hilaire asserts that no leeches are found in the Nile, and therefore supposes the Belle of the father of history were not leeches, but mosquitoes. But Savigny has described a leech under the name of Bdella nilotica, which he regards as synonymous with the leech of Herodotus. Bosc mentions one which was found in the stagnant waters in Egypt, when not inflated as small as a horse-hair, which very much annoyed the French soldiers, attacking them in nearly the same way; when they drank, fastening itself to their throat, and occasioning hemorrhages and other serious accidents.
Mr. Madox, in his Excursions in the Holy Land, Egypt, &c, states that he had frequently seen, on the banks of the Nile, a bird about the size of a dove, or rather larger, of handsome
1 See above, p. 164, 103, 110.
2 PLATE VIII. F10. 3.
plumage, and making a twittering noise when on the wing. It had a peculiar motion of the head, as if nodding to some one near it, at the same time turning itself to the right and left, and making its congé twice or thrice before its departure. This bird, he was told, was called Sucksaque, and that tradition had assigned to it the habit of entering the mouth of the crocodile, when basking in the sun, on a sand bank, for the purpose of picking what might be adhering to its teeth: which being done, upon a hint from the bird, the reptile opens his mouth and permits it to fly away.1
This seems evidently the Trochilus of Herodotus, above al luded to, as clearing the mouth of the crocodile from the leeches. Aristotle, in more than one place of his History of Animals, mentions such a bird, and a similar tradition concerning it, with that of Mr. Madox. "The Trochilus flying into the yawning mouth of the crocodile cleanses his teeth, and thus is provided with food. The latter, senisble of the benefit, suffers it to depart uninjured." In another place,3 he seems to speak of it as an aquatic bird, yet afterwards he describes it as frequenting shrubberies and subterranean places. Whether this animal really attends thus upon the crocodile has not been ascertained, but it would be singular that such a tradition should have maintained its ground so long without any foun dation.
As a farther proof that the Bdella of the father of history is a true leech, and not a mosquito,-as M. Geoffroy St. Hilaire, from the meaning of its primitive, would interpret the word,it may be observed that Aristotle compares the Bdella to an carth worm, and describes its peculiar motion; and in Hesychius it is said to be a kind of Scolex or worm; Theocritus also alludes to its blood-sucking propensities.7
That leeches infest the aquatic Saurians is farther evident from a letter received by Mr. R. Taylor, and very kindly communicated by him to me, from a friend at Calcutta, Mr. W. C. Hurry, who having observed that the fauces of the gigantic cranes were generally very full of leeches, determined to examine the crocodile; and upon a large alligator he found a small red species, of which he sent specimens. A friend of mine, Mr. Martin, of Islington, observed also that the alligators
1 Excursions, &c. i. 408.
3 Ibid. 1. viii. c. 3.
Hist. An. 1. ix. c. 6.
lbid. 1. ix. c. 11.
6 De incessu animal. c. 9.
5 Them. B to suck.
7 Idyll. ii. line 55, he calls it Aluvatis Bderna. 8 Ciconia Argala?
of Pulo Penang were infested, as he thought, by an animal of this kind, called by the natives its louse.
The Trochilus of Aristotle, Mr. Stanley states to Mr. Taylor, is the Egyptian Plover; who farther observes that the Green Tody is also related to cleanse the mouths of the alligators in the West Indies, from the gnats and flies that stick, in great abundance, in the glutinous matter they contain.
But there is a terrestrial kind of leech found in the island of Ceylon, which appears to be a greater pest than any other species of the genus, and one of the greatest scourges of that fine island. They infest, in immense numbers, the mountains, woods, and swampy grounds, particularly in the rainy season. They are oftener seen on leaves and stones than in the waters. The largest are about half an inch long when at rest. Their colour varies from brown, to light brown, with three longitudinal yellow lines. They are semi-transparent, and when fully extended are like a fine chord, sharp at the extremity, and easily thread any aperture, so that they can penetrate through the light clothing worn in that climate, rendering it impossible, at that season, to pass through the woods without being covered with blood. Dr. Davy counted fifty on the same person; no sooner does any individual stop, than, as if they saw or scented him, they crowd towards him from all quarters. From their immense numbers, activity, and thirst of blood, they are the great pest of travellers in the interior. Percival says that the Dutch, in their march into the interior, at different times, lost several of their men from their attack. Other animals besides man suffer dreadfully from them, and horses in particular are rendered so restive, when they fasten upon them, as to be quite unmanageable and unsafe to ride. The only way to prevent their attack, is to cover the skin completely.
The office devolved upon the present tribe, is one which, within certain limits, is beneficial to the animals who are the objects of it-though those last mentioned would be inserted in a list of the destroyers of the animal kingdom-which contribute to maintain a just balance between the different members of it. The fly that bites the horse prevents it from overfeeding, and so the leeches may be of use to the larger aquatic animals, at the same time that the smaller ones, such as the grubs of insects, must generally perish from the insertion of their sharp jaws, and the suction of their proboscis.
Yet as we see, this is one of the animals that man has taken into alliance with him, and this no doubt Providence intended
1 Charadrius Egyptius.
2 Thdus viridus.
he should, and probably directed him to it, I mean by causing certain circumstances to take place that attracted his attention and indicated its probable use. So that what at first put him to pain, and caused him alarm, he found, upon trial, might be rendered a very valuable addition to his means of cure when attacked by disease, or when he was suffering from a local injury.
The leech tribe, besides its utility in the exercise of its own function, may be useful as affording nutriment to some other animals, as fishes and birds.
The earth-worms1 form a principal feature of the next Order, and afford a delicious morsel to birds of every wing. The fisherman also baits his hook with them, and the ground-beetles often make a meal of them, so that had they no other use, still they would be a very important part of the creation. But their great function appears to be that of boring the earth in all directions, whereby they are useful to the farmer and grazier, giving a kind of under-tillage to pasture and other lands, and by the casts which they every where throw up, they help to manure the soil, and do the same for pastures, that the spade does for the garden and the plough for arable land, place the soil that laid below above. Their food being vegetable detritus, what passes from them must be very good
The anatomy of these well-known animals is very singular, and well worthy the attention of the physiologist and zootomist, the only circumstance relating to it that I shall here mention is that their long body is not only divided externally into rings, but internally into an equal number of cells separated from each other, if I may so speak, by a kind of dissepiment or diaphragm-there are more than a hundred of these cells in the common species, as appears by Mr. Bauer's admirable figures in the Philosophical Transactions for 1823, to which I must refer the reader for farther information on this subject, first observing that there seems some analogy between the cells of the earth-worm and the joints of the tape-worm.
The motion of these animals, and of many other Annelidans, is accomplished by means of the rings of their body and their lateral bristles; the latter the Creator has given to them, in the place of legs: pushing with the anterior portion of these against the plane of position, by contracting the rings, they bring up the posterior portion of their body, and then fixing
1 Lumbricus (Ent rion Sav.) terrestris. L. &.c.
2 Carabus. L.