drawing their corpuscular food within the vortex of their mouth is thus amusingly illustrated by Spallanzani. As a certain species of whale, says he, (sic magnis componere parva solebat) after having driven shoals of herrings into a bay or strait, by a blow of its tail produces a whirlpool of vast extent and great rapidity, which draws the herrings into its vortex; the monster then presenting its open mouth, the herrings are precipitated into its throat, and it is soon satiated : so the carnivorous Infusories produce a vortex by their tentacles, and satisfy their appetite.

I have been more diffuse upon the history of the animals whose functions in nature I am next to consider, because to them in a more particular manner, applies Pliny's observation with regard to insects. In his tam parvis, atque tam nullis, quæ ratio, quanta vis, quam inextricabilis perfectio! In nothing is the power and wisdom of their Almighty Author more signally conspicuous. Organization so complex, and life, and spontaneous motion, and appetite, and means to satisfy it, and digestion, and nutrition, and powers of reproduction in animals of such infinite minuteness! Who can believe it? Yet so it is, and that each of these should be varied in the different tribes and genera-that these less than the least of all the creatures that present themselves to the observation of mankind, and which till within a century or two were not suspected to exist, should

out-number beyond all statement of numbers, all the other animals together that people the whole globe, that they should probably enter into us and circulate in our blood, nestle between our teeth, be busy every where, and perceived no where, till the invention of the microscope drew aside the veil between us and these entities, and we saw how God had filled all things with life, and had based the animal kingdom upon living atoms, as well as formed the earth and the world of inert ones. But to us the wondrous spectacle is seen and known, only in part; for those that still escape all our methods of assisting sight, and remain members of the invisible world, may probably far exceed those that we know.

We may conclude that this vast, or rather infinite, host of animalcules was not created merely to be born and die; was not sown, as it were, over every part of the earth's surface, lurking in seeds, and other vegetable and animal substances, till coming into contact with fluid matter of whatever description it starts into life, and swarming in the ocean, and its tributary streams; it was not thus dispersed every where, either alive, or in a state to revive and live, but for some great purpose, for which its organization, structure and station amongst animals, particularly adapt it.

With respect to its immediate action upon the vegetable and animal kingdoms, it has been ascertained, as to many species, that they ascend

with the sap in vegetables,' and are found in the blood and excretions of animals, who knows but they may act an important part in the animal frame; somewhat similar to what devolves upon the larves of certain insects, with regard to stagnant waters, they may be depurators where they are thus employed, and contribute to preserve a healthy action. It is true, as far as vegetables are concerned, especially grain, they appear to destroy, where they take up their residence, but when we discover the same or similar species, in sour paste or vinegar, they seem destined to consume substances that cease to be wholesome; and in fact, in all fluids, in which they usually so abound, they may be destined to fulfil a similar office, and it is a remarkable circumstance in their history confirmatory of this idea that these animals, though animation in them is often suspended for a long time; when they swarm in infusions, having fulfilled their office, perish in a few days.

It is probable that in the waters of our globe an infinity of animal and vegetable molecules are suspended, that are too minute to form the food of even the lowest and most minute animals

Mr. Bauer found Vibrio Tritiri, in the stalk as well as in the ear and grain of plants of wheat, which were raised from seeds inoculated with it. Phil. Trans. 1823. 3.

See above, p. 152.

of the visible creation, and therefore an infinite host of invisibles was necessary to remove them as nuisances.

But the principal point, and that in which their utility most evidently appears, is their furnishing a principal portion of the food of innumerable animals of a higher order than themselves. Those infinite armies and forests of locomotive and fixed Polypes, that give to the ocean one of the features that distinguish earth, have their mouths surrounded with tentacles, when expanded assuming the appearance of so many blossoms, with these they collect their food, which, amongst the more minute ones, consists often of our Infusories. A single stem of these compound animals, having often innumerable oscula or mouths, requires a vast supply of food; others equally compound, as the Ascidians or Alcyons, by alternately absorbing and expelling the sea water, draw in with it a supply of animal food, consisting, in part, of the creatures in question, which abound in the oceanic waters; some of these have a common organ for this purpose, and in others each individual of the system is fitted with one; the Molluscans and an infinity of the smaller inhabitants of the ocean, doubtless also derive a considerable portion of their nutriment from them, the minute Crustaceans probably do the same, and many insects, whose larvæ inhabit the waters, some by pro

diate state.

ducing a vortex like the rotatories,' thus find an abundant supply to carry them to their intermeBut not only do these creatures furnish the more minute animals that inhabit the waters, with a considerable portion of their food, but, it should seem, even some of those that are of a higher grade, and larger stature. Whoever has been in the habit of keeping gold and silver fish, in glass or other vessels, is aware that they require no other food than a fresh supply of water every second or third day. Their nutriment therefore must be derived from what they find in the water. In this may often be seen minute Branchiopods swimming here and there, sometimes with a bundle of eggs appended to each side: but these are not sufficiently numerous to form the whole of their food, the water must therefore contain other nutritive substances which may contribute to their subsistence, and as it is known that various infusory animalcules inhabit it, we may conclude that they are inserted in their bill of fare. It has been observed by an eminent writer, speaking of the gold fish, "The water, when care is taken to renew it frequently, appears sufficient for the nutriment of these fishes during many months; but it should be considered that though this water appears to us very pure,

Culex, Stratyomis, &c. VOL. I.

2 Cyprinus auratus.

M