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ORDERS OF INSECTS.

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plants so completely as to produce the appearance of a discoloured change of structure.

The family of spiders (ara'nea) is not always arranged among insects, and strictly speaking their structure is dif ferent in some important particulars. They are distinguished from all other insects by the absence of the antennæ. They have generally eight legs, and are furnished with six or eight eyes, which enable them to see objects in several different directions at once. They are nourished generally by living prey, which they secure by means of a web, spun with much ingenuity. The threads, of which the web is composed, are produced from six little fleshy bunches, or muscular instruments, each of which contains about a thousand tubes, or outlets of threads, so extremely minute that many hundreds of them must be united before they form one of those visible ropes, of which the spider's web is composed. By means of their webs, many species of spiders, particularly when young, are able to transport themselves to a considerable distance through the air. In order to effect this, they ascend some eminence, and throw out a number of webs. These are raised up and carried along by the wind, and the animal being buoyed up by them is conveyed sometimes to a great height. In order to alight, they have only to disengage themselves from a part of their web, and suffer themselves to descend gradually to the ground. It is probable that they have recourse to this expedient, in part at least, for the purpose of catching insects for food. In autumn, the air is often full of the cobwebs which have been made use of for this singular mode of conveyance. fine filmy substance is called Gossamer; and it is seen not only in the air, but is more observable in stubble fields, and upon furze and other low bushes. Those who have ascended eminences for the purpose of observing the phenomenon, have frequently seen spiders floating by in the air, supported in the manner which has been described.

To the Insect of the Gossamer:-By C. SMITH.

Small, viewless aëronaut, that by the line
Of Gossamer suspended, in mid air

This

Float'st on a sunbeam. Living atom, where Ends thy breeze-guided voyage? With what design In ether dost thou launch thy form minute,

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CRUSTACEOUS ANIMALS.

Mocking the eye? Alas! before the veil
Of denser clouds shall hide thee, the pursuit

Of the keen swift may end thy fairy sail.

Thus on the golden thread that fancy weaves
Buoyant, as Hope's illusive flattery breathes,
The young and visionary poet leaves

Life's dull realities, while seven-fold wreathes
Of rainbow light around his head revolve.

Ah! soon at Sorrow's touch the radiant dreams dissolve. QUESTIONS.-1. Upon what is the division of insects into orders ounded? 2. What are the characteristics of the first order? 3. Second? 4. Third? 5. Fourth? 6. Fifth? 7. Sixth? 8. Seventh ? 9. Describe the wings of butterflies. 10. Describe ephemeral flies? 11. What is worthy of notice in ants, wasps, and bees? 12. How is the buzzing of flies produced? 13. How do aptera insects often appear on plants? 14. How are spiders distinguished from all other insects? 15. How is the web of the spider produced? 16. Describe the aerial excursions of spiders. 17. What is the gossamer, and where seen?

LESSON 101.

Crustaceous and Molluscous Animals.

Mu'cous, slimy, viscous or glutinous.

THE Crustaceous animals have been sometimes included in the class of insects, to which they have indeed many strong points of resemblance. They deserve, however, a separate consideration, both on account of their size and importance, and of some anatomical differences of structure. They have articulated limbs, antennæ, and jaws, similarly formed to those of insects. But they breathe by means of gills, and have a regular, double circulation; in which par ticulars they differ from insects. Among the most familiar examples of this class are the lobster, craw-fish, and what is usually called the horse-shoe. They are covered by a pretty thick, firm shell, which envelopes them completely. As this shell is incapable of growth, it is occasionally changed, to make room for the constant increase in size of the animal. It is thrown off, and their bodies remain for a time entirely naked, and exposed in a soft and defenceless state.

MOLLUSCOUS ANIMALS.

In this case, the animal generally retires to some place of concealment and security, and remains till the shell is restored by the deposition of calcareous matter on the external membrane of the skin, which becomes hard and firm, and finally takes the place of the old shell.

The Molluscous animals form a large and extensive class, but their structure, residence, and habits, are obscurely and imperfectly known. Among them are the cuttle-fish, oyster, clam, snail, and, in short, nearly all the testaceous animals, or shell-fish, as they are usually called, although they have no resemblance to fishes, and do not all inhabit the water. They are destitute of bones and articulated limbs. Their bodies are generally of a soft texture, and frequently, at first sight, appear to be little else than a simple mucous mass, without parts and almost without organization. In most instances they are completely enveloped in a fold or reflection of the skin, which is called their mantle. Sometimes there is only this simple membranous covering; but more frequently there is a hard external shell, which serves as a retreat into which the animal may withdraw itself, and which it can carry about in all its changes of place. These shells differ exceedingly in shape, colour, and texture, in different species, and among them are found some whose form, polish, and splendid tints place them among the most beautiful objects in nature.

QUESTIONS.-1. In what points do crustaceous animals resemble insects? 2. In what do they differ? 3. What are examples of this class? 4. What is said of the growth and casting of their shell? 5. What are examples of molluscous animals? 6. What description of them is given? 7. What is said of their shells? [NOTE. The study of those animals in the class mollusca which are characterized by a shell or calcareous covering has obtained the distinct scientific name of Conchology. The objects of conchology are separated into three divisions, namely, multivalves, or shells with many valves; bivalves, or shells with two valves; univalves, or shells with one valve.]

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ZOOPHYTES.

LESSON 102.

Vermes and Zoophytes.

Tentac'ula, often called feelers; organs supplying the place of hands and arms to some animals, and intended also for feeling. (Singular, Tentaculum.)

THE term Ver'mes has been used with great vagueness in natural history, and employed to designate animals to which the name was not appropriate. It is now, however, more restricted in its application, and is made to include only a small class of animals. Their bodies are of a cylindrical, elongated shape, divided into a great number of rings. In some species, certain black points appear around the head, which have been supposed to be eyes, but this is doubtful. They are the only invertebral animals which have red blood. It circulates in a double system of vessels, but there is no distinct fleshy heart to give it motion. They breathe by means of gills, which are sometimes within and sometimes without their bodies. They have no limbs, but on each of the rings of which their bodies are composed, are little spines or bristly projections which answer in some sort the purpose of feet. All, except the earthworm, inhabit the water. Many of them bury themselves in the sand; some form themselves a sort of tube or habitation of sand, or other materials; and others exude from their surfaces a calcareous matter, which produces a shell around them. When cut through the middle, each portion becomes a distinct individual.

There are several species of the leech, of which the medicinal leech is the most valuable. It has three jaws or rather lancets, with which it pierces the skin of animals, in order to draw their blood. Its tail is furnished with a shallow cup, by which it is able to fix itself firmly to different objects, while obtaining its nourishment; and by means of the same organ it moves from place to place.

The class of Zo'ophytes is the last division of the animal kingdom, and the lowest in the scale of the animated creation. It includes an immense number of individuals but imperfectly known, and having but few points of resemblance and connexion with one another. In general, they have no nervous system, no complete vascular circulation,

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no distinct apparatus for respiration, and no sense but that of feeling and perhaps that of tasting. This is not true, however, without exception; for, in some instances, traces of a nervous system, of a circulation, and of respiratory organs, may be detected, as in the sea-urchin, the common star-fish, and the sea-egg. These Zoophytes are the most perfect in their structure, and are endowed with a curious set of organs for the purpose of motion. Their shells are pierced with a large number of holes, regularly arranged, through which project the feet of the animal, or rather the instruments answering the purpose of feet. These are little hollow cylinders, filled with a liquid, and terminating in a kind of knob, which is also hollow. By forcing the liquid into these cylinders, or by exhausting it from them, the animal can either lengthen or shorten them. The knob, when exhausted, is drawn into a cup-like form, and thus may be firmly fixed to whatever object it is applied, like a cuppingglass; and when the liquid is again thrown into it, it is again loosened.

Pol'ypes have a hollow, cylindrical, or conical body, with one extremity open which serves for their mouth, and is surrounded by a number of organs, (tentacula) by which they seize their prey. Many of them have been celebrated on account of the fact, that when one is divided into several pieces, each piece becomes a distinct animal, perfect in all its parts. The immense beds of coral and the different kinds of sponge, are nothing but the habitations of infinite numbers of these little animals, and are produced by their labour. Corals grow in such quantities, and to such heights in some seas, as to create islands. The Friendly Islands, in the Pacific Ocean, were thus raised by corals from the depth of that sea. Ships have often been lost by striking on coral-rocks.

QUESTIONS.-1. What is said of the former and present application of the term Vermes? 2. What is said of the structure of Vermes? 3. Of the circulation of their blood and of their respiration? 4. Of their instruments of motion, and their habitations? 5. Describe the medicinal Leech. 6. What is said of the general structure of Zoophytes? 7. Describe the organs of motion in the most perfect Zoophytes. 8. What is the structure of Polypes? 9. For what celebrated? 10. How are corals and sponge produced? 11. What is said of the growth of corals in some seas? [NOTE. To the class of Zoophytes belong Intestinal worms, sea-nettles, or sea-anem'ones, Meduse, or sunfish, and

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