226

ORDERS OF INSECTS.

dragon fly, large and well known insects that frequent lakes and pools of stagnant water; the Ephem'eral flies, which pass two or three years in the states of larva and chrysalis, but whose existence as winged and perfect insects is limited to a single day; and the Ant-lion and Ter'mites, the former celebrated as the destroyer of the common ant, and the latter for the ravages they make in some tropical countries.

The fifth order (hymenoptera) has four naked membranous wings, but destitute of that delicate, netted structure, which belongs to the last order. The females have either a perforator or a sting. In the domestic economy and mode of propagation of some of the species, there are circumstances which excite our admiration and astonishment. The ant, wasp, and bee belong to this order. They live in societies, greater or less in extent and number; and prepare habitations and nourishment for themselves and offspring, with a forethought and provident care, excelled only by man himself. In some of the tribes of this order, there is, beside the males and females, a third sort called neuters, as among the ants and bees.

The sixth order (dip'tera) has only two wings, but beneath them are two cylindrical projections, which seem as if they were the rudiments of another pair. These have been called balancers or poisers, from being supposed to aid them in preserving an equilibrium during their flight. Between them and the wings themselves are found small membranous scales, one upon each side, against which the balancer strikes with great rapidity, whilst the insect is in motion, and causes that buzzing which is then observed. To this order belong some of the most troublesome and annoying of the whole animal creation, such as the various species of gnat, and the common fly. They are found in almost every part of the globe.

The seventh and last order of insects (ap'tera) includes a great variety that are destitute of wings. It is true that in the preceding orders are arranged many sorts of insects that are destitute of wings, but they are so arranged because in their general structure and habits of life they resemble the other members of the order. The Aptera, however, have

such resemblance, and are therefore placed by themS. Some animals of this order cover the surface of

228

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 founded? 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 particulars 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.]

20

230

ZOOPHYTES.

LESSON 102.

Vermes and Zoophytes.

Tentacula, 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,