As we write, we look upon a prospect which excites our wonder and interest. The eye sees a variety of form and structure presenting a combination of grace and delicacy hardly to be matched in the whole of Nature's domain. Within the compass of a small round disc or circle, we behold numerous beings, each consisting of a bell-shaped head mounted on a delicate flexible stalk. The margins of the bells are fringed with minute processes, resembling miniature eyelashes, and hence named cilia; and these processes wave to and fro with an incessant motion, by means of which particles of solid matter suspended in the water around are swept into the mouth of the bells. Suddenly some impulse moves the beings we are gazing upon to contract themselves, and as if by magic, and more quickly than the eye can follow them, the bell-shaped bodies shrink up almost into nothingness by the contracting power of their stalks. Soon, however, as the alarm disappears, the beings once more uncoil themselves, the stalks assume their wonted and straight appearance, the little cilia or filaments once again resume their waving movements, and the current of life proceeds as before.

The spectacle we have been describing is not by any means a rare or uncommon one, to the microscopist at least. We have merely been examining a tiny fragment of pond-weed and its inhabitants, floating in a thin film of stagnant water. Attached to the weed is a colony of those peculiar animalcules known popularly as 'bell-animalcules,' and to the naturalist as VorticellÆ. Yet common as the sight may be to the naturalist, it affords one example of the many undreamt-of wonders which lie literally at the feet, and encompass the steps of ordinary observers; and it also exemplifies the deep interest and instruction which may be derived from even a moderate acquaintance with natural history, together with the use of a microscope of ordinary powers.

The bell-animalcules are readily procured for examination. Their colonies and those of neighbour-animalcules may be detected by the naked eye existing on the surface of pond-weeds as a delicate white nap, looking like some lower vegetable growth. And when a portion of the weed is placed under the object-glass of the microscope, numerous animalcules are to be seen waving backwards and forwards in all their vital activity. The general appearance of each animalcule has already been described. The bell-shaped structure which, with its mouth turned uppermost, exists at the top of each stem or stalk, is the body. The stalk is never branched in these animalcules; and except in certain instances to be presently alluded to, each stalk bears a single head only. The structure of the stalk is worthy of special mention. The higher powers of the microscope shew us that within the soft substance or protoplasm, of which not only the stalk but the body also is composed, a delicate muscular fibre is contained. This fibre possesses the power of contracting under stimulation, just as the muscles of higher animals contract or shorten themselves. And by means of this structure therefore, the bell-animalcules, when danger threatens them, are enabled to contract themselves with great rapidity, the stalk itself shrinking up into a spiral form. The operation reminds one forcibly of some sensitive plant shrinking when rudely touched. The lower extremity of the stalk forms a kind of 'root,' by means of which the animalcules attach themselves to fixed objects, such as pond-weeds, &c.

The bell-shaped body is sometimes named the calyx, from its resemblance to the structure of that name in flowers. The edge of the bell possesses a very prominent rim, and within this we find the fringe of filaments or cilia, which in reality form a spiral line leading to the edge of the bell, where at one point is situated the mouth, represented by an aperture or break in the rim of the body. We have seen that the cilia create miniature maËlstroms or whirlpools in the surrounding water, which have the effect of drawing particles of food towards the mouth. The study of the bell-animalcules affords an excellent example of the gaps which yet remain to be filled up in our knowledge of the structure even of the lowest and commonest forms of life. No structures are more frequently met with in the animal world than the delicate vibratile filaments or cilia, so well seen in the bell-animalcules. The microscopist meets with them in almost every group of animals he can examine. They are seen alike in the gills of the mussel and in the windpipe of man; and wherever currents of air or fluid require to be maintained and produced. Yet when the physiologist is asked to explain how and why it is that little microscopic filaments—each not exceeding in many cases the five-thousandth part of an inch in length, and destitute of all visible structure—are enabled to carry on incessant and independent movements, his answer is, that science is unable, at the present time, to give any distinct reply to the query. No trace of muscles is found in these filaments, and their movements are alike independent of the will and nervous system; for when removed uninjured from the body of the animal of which they form part, their movements may continue for days and weeks together. What a field for future inquiry may thus be shewn to exist, even within the compass of a bell-animalcule's history—these animalcules being themselves of minute size, and even when massed together in colonies, barely perceptible to the unassisted sight!

A very simple and ingenious plan of demonstrating the uses of the cilia in sweeping food-particles into the mouths of the animalcules, was devised by Ehrenberg, the great German naturalist. This plan consists in strewing in the water in which the animalcules exist, some fragments of coloured matter, such as indigo or carmine, in a very fine state of division. These coloured particles can readily be traced in their movements, and accordingly we see them tossed about and whirled about by the ciliary currents, and finally swept into the mouths of the animalcules, which appear always to be on the outlook, if one may so term it, for nutritive matter. Sometimes when we may be unable to see the cilia themselves, on account of the delicate structure, we may assure ourselves of their presence by noting the currents they create.

The structure of the bell-animalcules is of very simple and primitive kind. The body consists of a mass of soft protoplasm—as the substance of the lower animals and plants is named; but this matter is capable of itself of constituting a distinct and complete animal form, and of making up for its want of structure by a literally amazing fertility of functions. Thus it can digest food; for in the bell-animalcules and their neighbours, the food-particles swept into the mouth are dissolved amid the soft matter of the body in which they are imbedded. Although the animalcules possess no digestive system, the protoplasm of the body serves them in lieu of that apparently necessary apparatus, and prepares and elaborates the food for nourishing the body. Then we have seen that the animalcules contract when irritated or alarmed. A tap on the slide of glass on which they are placed for microscopic examination, initiates a literal reign of terror in the miniature state; for each animalcule shrinks up as if literally alarmed at the unwonted innovation in its existence. This proceeding suggests forcibly to us that they are sensitive—if not in the sense in which higher animals exhibit sensation, at least in much the same degree and fashion as a sensitive plant. And where sensation exists, analogy would lead us to believe that some form of apparatus resembling or corresponding to nerves exercising the function of feeling, must be developed in the animalcules. Yet the closest scrutiny of the bell-animalcules, as well as of many much higher forms, fails to detect any traces of a nervous system. And hence naturalists fall back upon the supposition that this curious protoplasm or body-substance of these and other lower animals and plants, possesses the power of receiving and conveying impressions; just as in the absence of a stomach, it can digest food.

The last feature in the organisation and history of the bell-animalcules that we may allude to in the present instance is that of their development. If we watch the entire life-history of these animalcules, we shall observe the bell-shaped heads of various members of the colony to become broadened, and to increase disproportionately in size. Soon a groove or division appears in this enlarged head; and as time passes, the head appears to divide into two parts or halves, which for a time are borne by the one stalk. This state of matters, however, does not continue; and shortly one of the halves breaks away from the stalk, leaving the other to represent the head of the animalcule. This wandering half or head is now seen to be provided at each end with cilia, and by means of these filaments swims freely throughout the surrounding water. After a time, however, it settles down, develops a stalk from what was originally its mouth extremity; whilst the opposite or lower extremity with its fringe of cilia comes to represent the mouth of the new animalcule. We thus note that new bell-animalcules may be produced by the division of the original body into two halves. They also increase by a process of budding. New buds grow out from the body near the attachment of the stalk; these buds in due time appearing as young VorticellÆ, which detach themselves from their parent and seek a lodgment of their own.

These briefly sketched details may serve to interest readers in a comparatively unknown field of observation, accessible to every one who cares to know something of one of the many life-histories with which our universe teems, but which from their very plenty are seldom thought of or recognised. And the present subject is also not uninteresting if we regard it in the light of a corrective to those too commonly received notions, usually fostered by ignorance of our surroundings, that there is nothing worth attention in the universe but humanity and human affairs.