Page images
PDF
EPUB

*

THE LONG-ARMED AND GREEN POLYPE t.

These are two species which will fully illustrate the nature of the whole tribe. They are found in clear waters, and may generally be seen in small ditches and trenches of fields, especially in the months of April and May. They affix themselves to the under parts of leaves, and to the stalks of such vegetables as happen to grow immersed in the same water; and they feed on the arious species of small worms, and other aquatic animals that happen to approach. When any animal of this kind passes near a Polype, the Polype suddenly catches it with its arms, and dragging it to its mouth, swallows it by degrees, much in the same manner as a snake swallows a frog. Two Polypes may occasionally be seen in the act of seizing the same worm at different ends, and dragging it, in opposite directions, with great force. It sometimes happens, that, while one is swallowing its respective end, the other is also employed in the same manner; and thus they continue swallowing, each his part, until their mouths meet. They then rest for some time in this situation, till the worm breaks between them, and each goes off with his share. But when the mouths of both are thus joined together upon one common prey, a more dangerous combat now and

DESCRIPTION. The common, or Long-armed Polype is about an inch in length, of a yellowish-gray colour. It has usually around the mouth about seven tentacula, which are longer than the body. The general shape of the body is somewhat cylindrical, tapering towards the base.

SYNONYMS. Hydra grisea. Linn.-Hydre grise. Bosc.L'Hydre à long bras, in France.

+ DESCRIPTION. This species is of a green colour, and furnished usually with eight tentacula, which are shorter than the body. Like the preceding animal, it has the power of contracting its body, in a very sudden manner, when disturbed, so as to appear only like a small green or brownish lump. SYNONYMS. Hydra viridis. Linn.-Hydre verte. Cuvier.

Bosc.

then ensues. The largest Polype gapes and swallows his antagonist; but, what is extremely wonderful, the animal thus swallowed seems to be a gainer by the misfortune. After it has lain in the conqueror's body for about an hour, it issues unhurt, and often in possession of the prey that had been the original cause of contention. The remains of the animal on which the Polype feeds are evacuated at the mouth, the only opening in the body. The Polype is capable of swallowing a worm thrice its own size: this, though it may at first appear incredible, is easily understood, when we consider that the body of the Polype is extremely extensile, and is dilated on such occasions to a surprising degree.

The species are multiplied, for the most part, by a kind of vegetation, one or two, or even more youngones, emerging gradually from the sides of the parent animal; and these young-ones are frequently again prolific before they drop off: so that it is no uncommon thing to see two or three generations at once on the same Polype.

But the most astonishing particular respecting this animal is, that, if a Polype be cut in pieces, it is not destroyed, but is multiplied by dissection: it is thus literally

711

Rich from its loss, and fruitful from its wound.

It may be cut in every direction that fancy can sug-gest, and even into very minute divisions, and not only the parent stock will remain uninjured, but every section will become an animal. Even when turned insideout, it suffers no material injury; for, in this state, it will soon begin to take food, and to perform all its other natural functions.

M. Trembley, of Geneva, ascertained that different portions of one Polype could be engrafted on another. Two transverse sections brought into contact will quickly unite, and form one animal, though each section belong to a different species. The head of one

species may be engrafted on the body of another. When one Polype is introduced by the tail into another's body, the two heads unite, and form one individual. Pursuing these strange operations, M. Trembly gave scope to his fancy, and, by repeatedly splitting the head and part of the body, he formed hydras more complicated than ever struck the imagination of the most romantic fabulists.

These creatures continue active during the greatest part of the year, and it is only when the cold is most intense that they feel the general torpor of nature. All their faculties are then, for two or three months, suspended. But if they abstain at one time, they make ample amends in their voracity at another; and, like all those animals which become torpid in winter, the meal of one day suffices them for several months.

Animalcules*.

OF THE VORTICELLA TRIBE †.

The Vorticellæ, or Wheel Animals, are the most remarkable of all animalcules, not only in their structure, but also in their habits and production. In general form they bear great affinity to the polypes, having a contractile, naked body, furnished with rotatory organs round the mouth; and indeed many microscopical writers have denominated them Cluster-polypes.

* The animals of the Linnean order Infusoria are extremely simple in their form, and generally invisible without a magnifying power. They are chiefly found in infusions of animal and vegetable substances.

In this tribe the animals have a contractile, naked body, furnished with ciliate, rotatory organs.

They are almost invisibly minute, and, during the summer months, are generally found in clear, stagnant waters, attached to the stalks of the lesser water-plants, where they feed on animalcules still smaller than themselves. Many of the species are found in groups, sometimes formed by the mere approximation of several individuals, and at other times by the ramified or aggregate manner in which they grow. Their various motions, like those of the polypes, are generally exerted only for the purpose of obtaining prey. The rota

tory motion of their tentacula causes an eddy in the water, around each individual, sufficient to attract into its vortex such animalcules as happen to swim near; these the little creature seizes, by suddenly contracting its tentacula and enclosing them in the midst. In several of the species the stems, into which they occasionally withdraw themselves, are somewhat rigid or scaly. The young-ones are carried in oval integuments on the outside of the lower part of the stems; and, when ready to issue forth, the parents aid their extrusion, where such is necessary, by writhing their bodies, or striking the little vesicle. As soon as the young-one is liberated from its prison, it fixes itself, and commences the necessary operations to procure its food.

THE COMMON WHEEL ANIMALCULE*, AND THE
CONVALLARIAN VORTICELLA †.

If the water that is found standing in gutters of lead,

* DESCRIPTION. This very minute animal, which, to the naked eye, appears only like a yellowish dot, is of a somewhat cylindrical shape. It is furnished with a double rotatory organ; its tail is composed of about three retractile joints, and terminated by four minute hooks.

SYNONYMS. Vorticella rotatoria. Linn.-Vorticelle rotifère. Bosc.-Le Rotifère de Spallanzani. Cuvier.-Wheel Animal.

+ DESCRIPTION. To the naked eye the Convallarian Vor

or the sediment it has left behind, has any appearance of a red or dark brown colour, it will almost always be found to contain these animalcules. And, in the summer-time, if a small quantity of this dust be put into water, and placed under the microscope, it seldom fails to yield them in considerable numbers. They are denominated Wheel Animals, from their being furnished with a pair of instruments on the anterior part of their body, which, in figure and motion, somewhat resemble wheels.

These animalcules may be kept for several months out of water, and in a state of perfect dryness, without losing the principle of life. When dry, they are of a globular form, and about the size of a grain of sand. If put into water, after the space of about half an hour a languid motion begins. The globule turns itself about, lengthens by degrees, and soon afterwards becomes very lively. In a short time it protrudes its wheel, and swims about in search of food; or, fixing itself by the tail, brings the food to it by its rotatory organs, which throw the whole circumjacent fluid into a violent commotion. After its hunger is satisfied, it generally becomes quiescent; and sometimes resumes even its globular form.

During the time it is in action, it frequently changes its shape and appearance: this, and the sudden transformation of the head, are equally surprising and singular. From being very taper, the head sometimes becomes, almost instantaneously, as broad as any part of the body, and protrudes its curious machinery. The circular bodies projecting from the animal in this state, whirl round with considerable velocity. As they are very transparent, the edges excepted, which are set with numerous fibrillæ, it is difficult to distinguish how

ticella has the appearance of a white point. In the microscope it is seen to be bell-shaped, and not unlike the flower of the Lily of the Valley, each individual having a long retortile stem.

SYNONYMS. Vorticella convallaria. Linnæus.-Vorticelle muguet. Bosc. Cuvier.

« PreviousContinue »