Слике страница
PDF
ePub

far as màn is able to comprehend it, the plan of tho all-wise Creator.

THE HUMBLER FORMS OF ANIMAL LIFE.

a

Many of the humbler animals bear so close a resemblance to vegetables, that they were long supposed to occupy a sort of intermediate position between the two great provinces of organised nature. Hence they have received the name of zoophytes, or animal-plants. They are now included among the radiata.

At the very lowest point of the animal kingdom, we meet with a scries of creatures in which the functions of life are performed by a single cell and its contents. A good example is the amoeba, a singular microscopic animalcule, often found at the bottom of fresh-water ponds. This remarkable creature has the power of shooting out from all parts of its body finger-like projections, which serve the purposes of legs or arms. These it speedily draws in again, and extemporises fresh ones in rapid succession as it moves along, thus continually changing its shape, so as to justify the name of Proteus originally bestowed upon it. It has neither mouth nor stomach, yet we must not suppose that it keeps a perpetual fast. On the contrary, it seems to be, in its small way, of an exceedingly voracious disposition. When it meets with anything suitable for its support, the substance of the creature grows, as it were, round its destined prey, till the latter is fairly enclosed, after which it is gradually absorbed. The same extraordinary habits are met with in other varieties of unicellular animals.

Considerably higher in the scale of animated being are those aquatic creatures generally known as polypes. All of these are zoophytes.

Some of them inhabit the sea, as the sea-anemones ; · while others, as the hydra, are found in fresh water only.

The hydra consists of a long gelatinous cylinder, attached by one extremity to some aquatic plant (Fig. 12), and furnished at the other with very long tentacles, which it stretches about in the water in search of the minute ánimais on which it feeds. It is remarkable for its voracity. Like many other zoophytes, the hydra is proFig. 12, -TIIE HYDRA. pagated by a process of budding

or gemmation, the young animals growing out, branch-like, from the body of their parent. Strange as this may appear, there is a still more surprising artificial mode in which these creatures may be multiplied. If a living one be cut in pieces, it does not die, but each piece becomes a perfect animal. Portions cut off are speedily replaced, and wounds, however deep, heal up with marvellous rapidity. One of the most extraordinary facts connected with this creature is, that it may actually be turned

inside out, like the finger of a glove, without any derangement of its functions; the inner and outer skin exchanging places, and adapting themselves, without difficulty, to the performance of each other's functions.

The sea-anemone is in some respects similar to the hydra, but much more beautiful, and more complicated in its structure. It is most plentiful in tropical climates, but large numbers are also found on our own coasts, adhering to rocks and other submarine substances, Their tentacles (Fig. 13), being disposed in regular circles, and tinged with a variety of bright, lively colours, very nearly represent the petals of some of our most elegantly fringed and radiated flowers, such as the carnation, marigold, and anemone.

It is from this resemblance that they derive their name. They are almost equal to the hydra in voracity, and in the power of surviving and repairing an amount of injury that would be fatal to most other animals. If the upper part of a seaanemone's body be cut away, the base will produce a new mouth and tentacles, and proceed with its vital functions as

[graphic]

if nothing had happened. Nor is the part cut off less tenacious of life. On the contrary, a new base is gradually

FIG. 13.

[graphic]

developed, and in the meantime the tentacles are stretched out, and the mouth swallows its accustomed prey, apparently quite unconscious that it has no stomach to put it into! Yet this same creature, which seems so indestructible, may be killed in a few minutes by immersion in fresh water !

Such are a few specimens of the wonderful phenomena which the study of the humblest animals presents to us. Well may we say with the Psalmist, “O Lord, how manifold are thy works, in wisdom hast thou made them all.”

[ocr errors]

INSECTS.

INSECTS are the highest, and by far the most numerous class of the articulata. Their study forms one of the most interesting portions of natural history, and is, indeed, often treated as a separate science, under the name of entomology.

Like other articulata, their bodies are composed of rings or segments, which are usually thirteen in number, oue forming the head, three the thorax, and nine the abdomen.

The head is furnished with a curiously shaped mouth, two antenno, or feelers, and two large eyes of the most wonderful construction. These eyes are almost always of the kind called compound; they are composed of an immense number (sometimes as many as 20,000) of small convex lenses, each of which is supposed to be a distinct and effective eye. The thorax bears the organs of motion, which, in most insects, consist of six legs and four wings. Some species, however, such as the common fly and the gnat, have but two wings; and others, as fleas and bugs, are entirely destitute of these appendages.

Small as insects generally are, they play an important part in the economy of nature. They are the general scavengers both of the earth and atmosphere. Whenever the dead body of an animal is exposed, thousands of them assemble and bury it in their voracious stomachs. The filth and fetid matter which would otherwise poison all the springs of life, by filling the air with pestilential effluvia, supply to them the means of support. Nor are they less useful in checking vegetation, and preventing some of the more prolific vegetables from overrunning the whole surface of the earth. It must be admitted, however, that their ravages are often destructive as well as beneficial; and, in order that they may not entirely strip the earth of vegetation, it is necessary that they also should be kept in check. To effect this, one species is made dependent for sustenance upon another. Thus the ichneumon flies are the general enemies of the insect race. They introduce their eggs into the bodies of their victims, which thus, in due time, become a prey to the young ichneumons. Immense numbers of insects are also killed by frost, or picked up by birds ; so that, by a system of mutual checks, a constant equilibrium is maintained throughout the realms of nature.

Insects are propagated by means of eggs. Before arriving at maturity, many of these creatures pass through a series of changes of a very remarkable character. This metamorphosis, as it is usually called, is exemplified, in its complete form, in the case of beetles, moths, and butterflies,

[ocr errors]

all of which appear successively in three very

distinct stages of development. In the first, which is called the larva state, the insect has the form of a grub, maggot, or caterpillar. During this part of its existence, it eats voraciously, changing its skin repeatedly to make room for the rapid increase in its bulk. After a certain time, which varies greatly in different species, it begins to prepare for a period of quiescence. Having chosen a suitable resting-place, and perhaps wrapped itself in leaves, or in a cocoon spun from its own body, it again throws off its caterpillar skin, and there now remains only a small oviform mass, without mouth, eyes, or limbs, and exhibiting scarcely any sign of life. This is called a pupa or chrysalis.* In this state of torpor it exists for a longer or shorter period, after which, Fig. 14. Fig. 15.

Fig. 16.

*

[graphic]
[graphic][merged small][merged small]

Larya,

having arrived at maturity, it bursts from its prison in the full enjoyment of all its faculties. It is then said to be in the imago or perfect state.

This metamorphosis is one of the most striking phenomena in the history of insects, if it be not, indeed, the most marvellous thing in nature. To see the same animal appearing first as a soft worm-like creature, crawling slowly along, and devouring everything that comes in its way, and

* The figures here given represent, in its three different stages of development, one of the most useful insects—the silkworm. The leaf on which the larva is shown is that of the mulberry tree, its favourite food. It is from the cocoon or the chrysalis form that silk is obtained.

« ПретходнаНастави »