CHAP II.

WORMS.

Vermes. LINN.

SECTION I.

Introductory Remarks.

THE system of zoology that still continues most popular in our

own country is that of Linnæus, and we shall hence make choice of it in the prosecution of the present work. Under this system, the various classes of animals which it comprises may be contemplated in an ascending or a descending scale. Having commenced with inorganic matter, and meaning to close with the mechanical and other curious inventions of human intellect, we shall prefer the former of these views; and shall open with a few specimens of the lowest of the Linnæan classes, and which he has distinguished by the name of Vernies, or the Worm Tribes, the classific and ordinal characters of which we have already stated in the preceding chapter.

SECTION II.

[EDITOR.

Infusory. Worms or Animalcules; Wheel-animal, Eel vibrio, Trichoda, Monas.

THESE Constitute a division of animals which until the latter part of the 17th century, had escaped all human attention and investigation, and constituted a kind of invisible world: a series of beings, the structure, powers, and properties of which, are perhaps more astonishing than those of most other animals: yet of such minute

ness as, in general, to elude the sharpest sight, unless assisted by glasses. The ancients therefore were totally unacquainted with this class of beings. To them the mite was made the ne plus ultra, or utmost bound of animal minuteness; but the moderns, assisted by the invention of the microscope, have discovered whole tribes of animals, compared to which even mites may be considered as a kind of elephants. These minute beings are chiefly to be observed in fluids of various kinds; and principally in such as have had any animal or vegetable substances infused in them; and for this reason they are often called in modern zoology, by the title of animalcula infusoria, or infusorial animalcules. A most extraordinary idea was entertained by the celebrated Count de Buffon, relative to these animalcules; viz. that they were not real animals, but a kind of organic particles or moleculæ, which were capable, under certain circumstances, of being formed into animated beings. The experiments of Spallanzani and others have, however, completely over. thrown this chimerical and absurd theory of the Count de Buffon ; and indeed one would hardly think it possible for any person of unprejudiced mind, nay one may even add, of common sense, to view the several animalcules in fluids, and at the same time to doubt of their being real animals. Their rapid and various motions; their pursuit of the smaller kinds on which many of the larger prey; their avoiding each other as they swim; the curious and regular structure of their bodies; and their whole appearance, form the most convincing proofs of their real animal nature and life.

Animalcules, as before observed, are most frequently found in fluids; but this is a doctrine that has not always been clearly understood, and has been productive of some erroneous ideas in natural history. Some writers, for instance, have asserted that almost every kind of fluid abounded with animalcules; and that wines and spirits exhibited legions of them. This, however, is so very far from the truth, that none are ever to be discovered in inflammable spirits, or in any fermented liquor that has not passed either into the state of vinegar, or that is not grown completely vapid. As almost all extraordinary discoveries are liable, when related by unskilful persons, to have their circumstances exaggerated by additional ornaments, we need not be surprized that this has been the case relative to the history of microscopic animalcules. No sooner did the microscopical observations of Leewenhoeck and a few others

become pretty generally known, than immediately, as if by a kind of fatality, the animalcular doctrine was carried a great deal too far: and innumerable substances were supposed to swarm with these minute beings, which later and more accurate observations have proved to be totally free from them. Thus, the blueish or bloomy appearance on the surface of several sorts of plumbs, grapes, and many other fruits, has been supposed owing to innumerable legions of animalcules on the surface of the fruit: but this idea is entirely erroneous. It happens, a little unfortunately, that Mr. Pope has introduced it into his celebrated poem, the Essay on Man, which still continues to propagate the mistake amongst those who are not scientifically conversant in such subjects.

"Ev'n the blue down the purple plumb surrounds,

« A living world, thy failing sight confounds."

The blueish appearance above-mentioned is a mere vegetable efflorescence, which regularly takes place on such kind of fruit, and consists of particles of no determined shape, and has not the least appearance that could lead to a supposition of its being of an ani. mal nature.

To attempt a methodical enumeration of animalcules appears, at first view, almost a hopeless labour; since exclusive of the vast variety of species, (of which, in all probability, only a small part has yet been observed), many of them have a power of changing their shape at pleasure: so as to appear widely different at particular times from what they did the moment before; and others, though their form is constant, are apt to vary in colour; by which means some deception or obscurity may arise, and an uncertainty in determining the species. Much, however, has been done: a great many species of animalcules have been perfectly well described, and are perfectly well known to microscopical observers, since they possess characters too clear and plain to admit of any doubt of their species, whenever they happen to appear.

As examples of this curious and interesting race of animals, we shall particularize a few of the most remarkable kinds, and such as are well figured in the works of naturalists.

Among these the genus called vorticella is one of the principal: Its character is, that the mouth or opening is surrounded by nume

rous short feelers, forming a kind of fringe round the head. One of the most elegant species of vorticella is the vorticella convallaria, a beautiful transparent animalcule, the body of which is formed like a bell-shaped flower, and is furnished with a very long tail or stem, by which it affixes itself to whatever substance it pleases. When a groupe of these animalcules is viewed by the microscope, it exhibits the appearance of a set of animated flowers, alternately stretching out their stems at full length, and again suddenly contracting them in a spiral twist. This species is very common, and is generally found attached to the stems and under surface of the leaves of the common lemna minor, or duckweed.

But a still more elegant species is the vorticella racemosa. It is found during the summer months in clear stagnant waters, attached to the stalks of the smaller water plants, and other objects; to the naked eye the whole groupe, on account of the great number of individuals composing it, is distinctly visible, in the form of a small whitish spot, resembling a kind of slime or mouldiness, but when placed under the microscope in a drop of water on a glass, its extraordinary structure is immediately perceived. From a single stem proceed, at various distances, several smaller ramifications, each terminating by an apparent flower, like that of a convolvulous, and furnished on the opposite edges, with a pair of filaments resembling stamina. The whole is in the highest degree transparent, and perfectly resembles the finest glass; while the varying motions of the seeming flowers, expanding and contracting occasionally, and turning themselves in different directions, afford a scene so singularly curious, as to be numbered among the finest spectacles which the microscope is capable of exhibiting. Each animal, though seated on the common stem, is complete in itself, and possesses the power of detaching itself from the stem, and forming a fresh colony from itself.

To the genus vorticella also belongs the celebrated animalcule called the wheel-animal, from the appearance which the head in some particular positions exhibits; as if furnished with a pair of toothed wheels, in rapid motion: this animalcule, which is called vorticella rotatoria, has long ago been pretty well described and figured by Baker, in his work on the microscope: it is of lengthened shape, and of a pale brown colour, and is of such a size as to be sometimes perceptible by a sharp eye, even without a glass. It

is remarkable for its strange power of reviviscence, or restoration to life and motion, after being dried for many months on a glass. The wheel animal is often found on the scum covering the surface of stagnant waters, but more frequently in the water found in the hollows of decayed trees after rain.

In spring and summer, nothing is more common than to see the surface of the smaller kind of stagnant waters covered with a fine deep-green scum; and frequently the same kind of greenness is dif fused throughout the whole body of the water: this green colour is entirely owing to an animalcule of a genus called cercaria *. It has of late been described under the name of cercaria mutabilis, or changeable cercaria, because a variety sometimes occurs of a red colour. The animal is of a lengthened oval shape, with a slightly lengthened tail, the body or middle part appearing as if filled with very numerous green spawn or ova, while the extremities are transparent. It occurs at this season of the year in almost every puddle. The red variety is far less common, and the appearance which it exhibits is such as to alarm the superstitious with the idea of the water being changed into blood; a panic of which numerous instances have been adduced by authors; and which is the more excusable in those who are ignorant of the cause, as the animalcules are so very small as to be utterly imperceptible, except to an uncommonly acute eye, without the assistance of the microscope; so that even taking, up, and examining it, affords no satisfactory elucidation to the vulgar. Not unfrequently we have seen the whole surface of a large pond thus covered with this animalcule, of which there was not the least appearance the preceding day. It should be observed that some other animals, and particularly some small insects of the genus monoculus, have occasionally produced a similar appearance: but in that case the demonstration becomes easy; since every one, on taking up the water, perceives the red insects. We are assured by Swammerdam, that the whole city of Leyden was one morning in a state of consternation, on discovering that the waters of that place were ap ́parently changed into blood; but the philosopher soon had the satisfaction of undeceiving the people, by demonstrating to them the real cause.

Among the most remarkable of the animalcular tribe may be

Naturalist's Miscellany, vol. iii. pl. 107.