Графични страници
PDF файл

Daphnia, also instituted by Muller, on the ruins of Mtnoculus, includes those crusraceous animals which hare ramified anttntue. and one eye. From the results of the examinations of Levmenhoeck, bieedkam, Sivammetdam, Sehatffer, de Geer,, Geoffroy, Muller, and Jurine, we learn, among various other details, that these creatures have a constant rotatory motidn in their solitary eye; that they cast their shelly and transparent case every spring -, that, during that season of the year, they are oviparous, but viviparous in summer; that they vary in colour, being sometimes of a reddish white, sometimes greenish, and sometimes quite red, so as to induce the vulgar to believe that the water in which they reside has been converted into blood; that they are chiefly observed in spring and autumn; and that myriads of them are cut off by predatory birds and insects, but especially by the summer droughts, which dry up their native element. In the species pulex, (Monoculus pulex Lin.) one act of sexual union suffices for 6ix successive generations.

The attributes of Cypr'u are, pencilled antenna, and one eye. Several of the animals now included under this title have been described by Joilot, Backer, Ledermuller, and Geoffrey: but Muller formed them into a genus, and considerably widened its range. In all of them, the case bears a near affinity to a bivalve shell, which, by means of a ligament, opens and shuts at the pleasure of the animal. All the species inhabit stagnant waters, especially such as yield abundance of conferva, lemna, and other aquatic plants. According to Base, some of them possess the singular property of shutting themselves up in their case, and retiring into the mud, till the water evaporated by the heat is replaced. They swim by means of their antenna, which may be regarded as real fins, and which are susceptible of various combinations of motion. Like other tribes of this class, they cast their covering j a process which de Geer had occasion to observe, and which he has well described.

Cytbere, which is nearly related to the preceding, is chiefly distinguished from it by hairy antenna, by the absence of a tail, and by different habits. The five species, we believe, were all discovered by Muller, who also formed the genus. They are all marine animals, mostly haunting fuci, conferva, and various zoophytical productions; among which they may be seen running nimbly in search of food.

5. Pseudopoda. Head confounded with the first ring of the body} feet apparently useless for walking. This order contains two genera, viz. Cyclops, with a lengthened body, and one eye; and Argulust with the body ovate, and two eyes. Atnymone


*nd Naupliui of Muller are, according to the recent observations of Jurint, on'v young individuals of Cyclops. Even Argulus appears to be of doubtful formation j and.we may be allowed to observe that very considerable difficulty attends the investigation of these microscopical animals.

6. Ctphalota. Head distinct from the body. The genera are, Polyphemus, Zoea, and Branchiopoda.

* The form of the body of Polyphemus is very singular. The head is round, composed of a scaly envelope, which invests a large mass, -almost entirely black, moveable in all directions, in the interior of the head, and forming the only eye. The size of this organ is equal to a tenth part of the animal itself, which is an excessive proportion. Various small black lines proceed from its surface to the circumference of the scaly envelope, which we have just mentioned.

* This animal's body is divided into two parts by a strangulation. The first part, which de Geer terms the thorax, is the connecting point of the antenna, feel, and tail. The second, which he terms tbdomen, contains the eggs and the young.

* Its antennt, or rather the arms, (that we may 3till preserve de Gter's phraseology,) are attached to the two 6ides of the thorax, and nearly about its middle, or at a considerable distance from the head. They are composed of a long cylindrical stem, articu'ated to the thorax, and diverging into two branches, equally moveable, of considerable length, and formed of five joints, furnished with their long hair-like filaments, four of which issue from the articulations, and the three others from the extremity of the last joint. These seven filaments, which are moveable as the branches themselves, have a joint in the middle, which separates them into two parts, and adds to their flexibility.'

The transparency of the crust enabled de Geer to observe some of the internal parts, viz. the heart and the large intestine, as well as the existence of the young, in opposition to those who maintained that the Polyphemus was the larva of an inject. We suspect, however, that the male has never been examined.—The only species is oculus. (Monoculus ocuhss Lin.)

Zoea is distinguished by two very large sessile eyes, a thorax, and feet that are simply hairy, and formed for swimming. Bosc first established this genus, in consequence of having discovered the sole species, pelagica, thn as yet belongs to it. This extraordinary animal, which he found only once, in the passage from America to Europe, and about six hundred leagues from the latter, is transparent like glass, and is rendered visible in the water by its eyes, and a small green spot. When its tail is folded up, it has tne appearance of a globule, scarcely one quarter of a line in diameter, and traversed by a spine. It moves in all directions with wonderful velocity, and often turns eo itself. Its feet aie so minute, that they are discernible only

in consequence of their incessant action. Somewhat analogous to this species appears to have been the water bull, or Jlea, detected in th- sea by Slabber, and described with much interesting minuteness by that ingenious naturalist.

Branchiopoda. Two eyes placed on peduncles, body composrd of a srries of rings, feet with foliaceous appendages. The only species is the stagnails, corresponding to Cancer ttagnalis of the Linnean system. The particulars of its structure and hist' ry, as far as they are known, are ably stated by the younger Desmaret s wtio likewise assisted the author in his illustrations of sever 'i of the genera.

II. MAtACOSTRACA. '1 he introduction to this second division of the Crustacea contains much excellent information, relative to the distinctive characters laid down by antient and modern zoologists, external and interml organization, habits, and modes of arrangement.—With respect to the first of these topics, we shall only observe that the author renders ample justice to Aristotle, who seems to have been better acquainted; with the history of this family of animals th:;n of any other j and also to Lefranrq de Berkley, a Dutch writer, whose name is hardly known to naturalists, though he was the firpt among the moderns who has treated of the Crustacea as distinct from Insects. The anatomical details are stated with too much precision to admit of abridgement, and would, at any rate, he scarcely intelligible without the aid of the plates: but we consider them as forming a very important part of this preliminary dissertation. The view of the economy of these animals, which is here exhibited, is also well calculated to fix the attention of the curious inquirer. The striking pliaeztomena of the gradujl re-production of their lost or mutilated claws, and of their annua! moulting, or change of covering, including that of the stomach, ?.re sufficiently established by a recital of conclusive observations and experiments. We are likewise informed that the greatest number of Ma'atostraca live either solitary, or in snull groupes, though some congregate in immense crowds, and are not easily compelled to relinquish their favourite haunts. 1 hey have the faculty of walking, or swimming, either forwards or backwarks, or even in a lateral direction. Some species leap and spring ■with surprizing agility, and others march with such rapidity that a man can scancly overtake thrm. Though frequently found among marine and aquatic plants, they are purely carnivorous, and subsist on dead or living animals. They abound most on the shores of America and the East Indies, where they sometimes attain to a great size, and are often troublesome, from the slowness of their growth, it has been


inferred that some of them are capable of living during a whole century: but they are exposed to such multitudes of enemies, to such a variety of accidents, and to such a constitutional crisis in the moulting process,,that few are supposed to die of old age j and myriads are devoured by fishes, birds, and even mollusca, in the early stages of existence, when they are incapable of self-defence. Thus, by a wise provision of nature, a long-lived,1 carnivorous, and prolific race, which, if abandoned to the uncontrouled energies of its own resources, would soon over-run large districts, has bounds set to its multiplication and ravages, and administers at the same time to the sustenance of other tribes* Some of them furnish a nutritive and delicate food to the human species: but others are reputed dangerous, either from the purgative quality of their eggs, or from some unknown cause. In some parts of the West Indies, the inhabitants attribute this noxious property to the juice of the Manchineal (Hippomane ManctniUa\ but Jacquin has assured us that the animals never touch this fruit; and the most recent observations seem to prove that they are solely carnivorous. Some of the crabs about the island of St. Domingo, it has been alleged, contract a deleterious quality from coming in contact wich submarine copper veins: but this hypothesis requires confirmition.— As the larger eatable sorts are liable to speedy corruption after death, it is customary to boil them alive; and, in order to prevent the separation of the limbs from the body by the imprt-ssioa of sudden heat, the cook too often protracts their sufferings.

* If exposed for some time to the air, the m.ilacostracous animals become dry, and may thus be formed into collections: but this method is .liable to serious inconveniences. 1' the weather be hot and moist, their flesh rapidly decays, and blackens; thtir articulations separate, and their limbs fall asunder from the trunk : to which disadvantages we must add the offensive smell which they emit when in this state. Moreover, the larvx of anthrcna and dirmcslcs and those of some other insects, find in the fleshy substance of the body, though dried, a favourite aliment; and they insinuate themselves into it' in great numbers, and, gnawing all the cartilaginous menibran> s which connect the articulations, finally sever all the pieces rrom ..ne another. It is, indeed, possible to cement all these fragments, but not without much trouble and waste of tiiiie. We would, therefore, preferably recommend the plan of emptying them as completely as circumstances will admit, and subjecting them to the moderate heat of an oven. The disunion of the joints might, at the san e tine, be obviated by passing wires through the ctaws, especially the two fore claws; and destructive insects must be kept at a distance by the preservative of which we gave the recipe in the second volume of this history. Owing to the very frag'le nature of their antenna and limbs, the conveyance of these animals requires so much precaution,


that I would even advise those persons who arc desirous of transporting them, and travellers, to spare themselves the trouble of the above preparation, and to follow the method prescribed by Bote. Let each crab, when yet alive, be wrapped up in a piece of linea cloth, and put into diluted spirit of wine, in which a large quantity of soap has been dissolved. When these animals have reached their destination, they ate to be taken out of the barrel or vessel in which they were contained, and, after having their feet, anttnne, &c extended, they should be dried in the shade, and then permanently placed in glazed drawers, or cabinets constructed for the preserva* tion of insects. Crustaceous specimens, thus prepared, are not liable to the attacks of insects, their articulations are conveniently consolidated, and their colours are less subject to change, than when thty are prepared in the other way. The small Crustacea should be put into spirit of wine, and allowed to remain in it, because desiccation would quite disfigure them.'

Crabs may be kept alive for a considerable time in a moist place, or among fresh vegetables: but care should be taken not to cover them with water which cannot be frequently renewed ; since they quickly exhaust all the air contained in it, and consequently cease to breathe. They will live much longer when their feet only are plunged in water} for then they breathe the external air.

Without staying to particularize the methods proposed by other naturalists, we shall now glance at that which M. LaTreille has chosen to adopt and illustrate.—His characters of the Malacostraca are, 'palpigerous mandibles, several rows of pieces in the form of palpi or jointed jaws, in the mouth; four tntenna, of which none are branchial; from ten to fourteen feet, solely destined for motion; tarsi with a corneous hook at the extremity; covering or annular segments of the body, calcareous; eyes often pedunculated, and always two in number.'—Animals of this description he distributes into two orders, viz. Decapoda and Brancbiogastra. In the first, the head is confounded with the thorax, and the feet are ten in number; while in the second, the head is distinct, the gillg are external, and the number of feet generally exceeds ten.

i. The Decapida are subdivided into two sections, namely", the Bracbyura, with the tail shorter than the body, terminated by a single piece, and destitute of foliaceous appendages at the end; and Macroura, having the tail at least the length of the body, and terminated by several foliaceous appendages. This order is farther dissected into families, and groupes of families, and modifications of these groupes: but we shall be contented to hint at the more important construction of thsj genera. Of these the first is Cancer, with the crust little raised, and the feet on one line; a definition which obviously


« ПредишнаНапред »