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in water, which, says Professor Owen, “are the most minute, and apparently the most insignificant of created beings. Many of them are so diminutive that “a single drop of water may contain five hundred millions of individuals, a number equalling that of the whole human species now existing upon the surface of the earth.' Nevertheless the varieties in size are such that the difference between the smallest and the largest is greater than between a mouse and an elephant,' though even the elephant of the race is altogether invisible to the naked eye. They are the most widely diffused, and by far the most numerous of all the forms of organised life;' and whether in fresh water or in salt, there is hardly a drop of spray flung from the paddle of a steamboat which does not contain some specimens of the race. They pervade every clime-torrid, frigid, and temperate—and extend their reign in the northern latitudes beyond that of the vegetable kingdom. The part which Professor Owen, from whose lectures we borrow the whole of our statements on the point, represents them as performing is calculated vastly to extend our ideas of the wonderful economy of the universe.
• When we consider their incredible numbers, their universal distribution, their insatiable voracity, and that it is the particles of decaying bodies which they are appointed to devour, we must conclude that we are in some degree indebted to these active scavengers for the salubrity of our atmosphere. Nor is this all : they perform a still more important office in preventing the progressive diminution of the present amount of organised matter upon the earth. For when this matter is dissolved or suspended in water, in that state of comminution and decay which immediately precedes its final decomposition into the elementary gases, and its consequent return from the organic into the inorganic world, these wakeful members of nature's invisible police are everywhere ready to arrest the fugitive organised particles and turn them back into the ascending stream of animal life. Having converted the dead and decomposing particles into their own living tissues, they themselves become the food of larger Infusoria, as, for example, the Rotifera, and of numerous other small animals which in their turn are devoured by larger animals, such as fishes; and thus a pabulum, fit for the nourishment of the highest organised beings, is brought back by a short route from the extremity of the realms of organic nature.'--Lectures on Comparative Anatomy, Invertebrate Animals, p. 36.
Nor do their functions end here. Various species of these far less than specks, are protected by shells, the remains of which form vast beds on the surface of the globe, extending sometimes to nearly thirty feet in depth, and to a mile or two in length. •Truly indeed,' says Ehrenberg, as quoted by Professor
Owen, 'the microscopic organisms are very inferior in individual energy to lions and elephants, but in their united influences they are far more important than all these animals.' Leslie calculated that if the entire population of the world was estimated at eight hundred millions, which is far beyond the truth, and that one-half of the number were capable of work, the power employed by nature in the formation of clouds would still be two hundred thousand times greater than the combined exertions of the whole human species. The evaporation nevertheless by which the air is saturated with moisture, and which represents this stupendous force, is carried on without noise or disturbance, and is almost unnoticed by the larger part of mankind. The gigantic operations of the Infusoria are still more quiet and secret, The very existence of these creatures was unknown till Leeuwenhoek detected one in 1675, and it is only through the microscope that we become conscious of their being at all. So mighty are the agencies hidden in nature, so immeasurable the results which are worked in a stillness, and, as far as our unassisted vision is concerned, in a darkness as deep as that of the night. Their own life sustained by the products of death, the Infusoria are destined themselves to perish that they may sustain the frames of the creatures above them, death continuing to support life throughout the graduated scale of existence, until, the circle run, the food once more comes back to be the nutriment of animalcules from whom it originally proceeded.
The flesh-fly is another indefatigable scavenger. A small mass of decaying flesh sends forth an intolerable stench, and the sum total of the animal matter which is cast upon the earth would accumulate till it offended our senses and affected our health, were it not for the millions of busy beings which are deputed to clear it away. With such unerring instincts do they seek out their prey, and so commonly is putrefaction found to be teeming with life, that the creatures which spring up in it were once supposed to be generated by the corruption itself. This was long the stronghold of the atheist. Among the nobler animals the offspring had manifestly proceeded from parents to which they bore an exact resemblance. The incredulity of impiety, which flings aside the cable as too flimsy to hang upon and eagerly clutches at a rope of sand, turned away eyes which were wilfully blind from the palpable wonders of the universe, and looked for an explanation of the origin of life in the maggots which crawled in a rotting carcase. These the atheists maintained were clearly the creatures of unintelligent nature-creatures which evidenced design, and yet were brought into being without a designer. The natural history of this miserable school was as much at fault as their theology.
Redi covered vessels of putrid substances with paper or fine lawn, which kept out the insects, and nothing was produced. When the covers were removed, he watched to see what insects fed upon the aliment and laid their eggs in it, and the only creatures generated were of the identical species which had frequented the flesh-pots. Thus he proved that maggots were no more spontaneous products than whales and elephants, as Malpighi, by protecting earth from the imperceptible seeds which are scattered about by the winds, demonstrated that no plants spring up which are not first sown, and that consequently, to use the noble language of Bentley, 'they were all raised at the beginning of things by the Almighty gardener, God blessed for ever.' Some species of flesh-flies deposit their young already hatched; others, say Kirby and Spence, cover the nutriment with millions of eggs. In either case the progeny feed with an unexampled voracity. They increase their weight two hundred-fold in twentyfour hours, and Professor Owen states that there is no exaggeration in the assertion of Linnæus that three flesh-flies would devour the carcase of a horse as quickly as would a lion. The larvæ of the cockchafer remain for four years in the condition of grubs. The eggs of the flesh-flies turn to maggots in a couple of days, and in five days more arrive at their full growth, when they speedily pass into the chrysalis state. Had they continued in their primitive form, like the cockchafer, the food in which they were born would have failed them, and they would have died of inanition. But they have another office to perform in nature besides that of clearing away putrid remains, and therefore, to preserve them for this second purpose, as well as to keep the
race, their grub existence is brief and they come forth in a week or two perfect flies. Mr. Rowell has calculated that from a single specimen there would proceed in six generations sufficient flies to cover the world to the depth of about a mile and a quarter.
That they do not swarm notwithstanding is because they are destined to be the sustenance of innumerable birds, bats, and creeping things. They feed upon death, and sport their hour, when the stomach of some creature, which must eat them or starve, becomes their tomb.
The vegetable kingdom is the support of an infinity of creatures which escape our ordinary observation. On the oak,' says Dr. Carpenter, not less than two hundred kinds of caterpillars have been estimated to feed, and the nettle which scarcely any beast will touch maintains fifty different species of insects, but for which check it would soon annihilate all the plants in its neighbourhood.' The check is constantly requiring to be checked itself, and still the plan prevails of making the death of a super
abundant population sustain the life of some other description of beings. The caterpillars which are hatched from the eggs of the common white butterfly, and which may be seen feeding by scores upon cabbages, are kept down by the ichneumon fly. The singular process by which this is effected we give in the words of Professor Owen.
• The ichneumon, by means of her peculiarly long, sharp, and slender ovipositor, pierces the skin of the larva, and in spite of its writhing and the ejection of an acrid Auid, she succeeds in introducing the instrument by which the ova are transmitted, and lodged under the skin ; she then flies off to seek another. Sometimes the female ichneumon, when she has found a larva, seems to take no notice of it, and in that case it has been found that another ichneumon has previously oviposited there, and by some peculiar sense she ascertains that there is no room for more ova, or not food enough for them when hatched. After the ichneumon has deposited the ova, she plasters over the wound with colleterial secretion. When hatched, her larvæ subsist upon the fat of the caterpillars which they infest. They avoid penetrating the alimentary canal, but evidently destroy many of the minute branches of the trachea which ramify in the adipose tissue. Such wounded tracheæ probably permit the escape of sufficient air for the respiration of the parasitic larvæ ; for though the caterpillars so infested survive and go into the pupa state, they are uneasy and evidently diseased ; the loss of the adipose store of nutriment prevents the completion of the metamorphosis; they perish, and instead of a butterfly, a swarm of small ichneumons emerge from the cocoon.'Lectures on Comparative Anatomy, pp. 417, 432.
Surprising is the instinct which teaches the larvæ of the ichneumon to avoid eating the intestines of their living prey. Were they to devour its vitals they would terminate its existence and put an end to their own. Whatever may be the value of the cabbage to man, he probably owes it to the ichneumon fly that any portion of this vegetable falls to his share, for out of thirty caterpillars of the white butterfly which Reaumur placed under a glass, twenty-five were the habitation of their murderous foe. That these were devoured in the morning of their life is in accordance with the general law which enacts that some of every race that breathes should perish in their infancy, while others should last to middle age, and a few fill up the full measure of the days allotted to their kind.
The grub of the cockchafer commits great ravages both upon grass and corn by gnawing the roots of the plant.
Entire meadows are sometimes denuded by it. The rook eats these destroyers by thousands, and by one act gets food for himself, and protects the wheat which is the staff of life to man. They are the grubs which chiefly attract him to follow the plough, and when he plucks up a blade of grass or corn it is almost invariably for the sake
of some description of worm which is preying upon its root. The plants which he eradicates will be found upon examination to be dead or dying, and by devouring the cause of the mischief he saves the rest of the field from blight. Unobservant farmers, who never look beyond the surface, often mistake the policeman for the thief. Luckily their power to injure their benefactor is not equal to their will, or they would exterminate him altogether, and leave the depredators unmolested to consume the whole of the crops.
When an unhappy success has attended efforts of the kind the evil consequences have been signal and immediate. After the inhabitants had contrived to extirpate the little crow from Virginia at an enormous expense, they would gladly have given twice as much to buy back the tribe. A reward of threepence a dozen was offered in New England for the purple grackle, which commits great havoc among the crops, but protects so much more herbage than he destroys that the insects when he was gone caused the total loss of the grass in 1749, and obliged the colonists to get hay from Pennsylvania and even to import it from Great Britain. A few years since an Act was passed by the Chamber of Deputies to prohibit the destruction of birds in a particular district of France. They had been recklessly killed off, and the harvest being swept away in its first green stage by millions of hungry reapers, the earth had ceased to yield its increase. Extensive inroads like these upon the economy of nature reveal to us its wisdom, and clearly show us that if one while it is a blessing that particular animals should eat, at another it is a benefit to the world that they should be eaten. A flight of rooks renders services which could not be performed by all the cultivators of the soil put together, and if the poor birds are occasionally mischievous they are richly worthy of their hire. Make the largest probable allowance for their consumption of a portion of that crop, the whole of which they preserve, and they are still immeasurably the cheapest labourers employed upon a farm. Pages would be required to tell all the mistakes which are committed in the blind rage for destruction, and in the readiness of the lord of the creation to believe that everything which tastes what he tastes is a rival and a loss. Even
which find no friends, chiefly because they are armed with a sting, which, unlike man, they rarely or ever use unprovoked, are an important aid in keeping certain tribes within bounds. Mr. Rowell had two nests in a glass case, and found that the food brought in was chiefly caterpillars and insects. “Reaumur bas observed,' write
* ' Kirby and Spence, that in France the butchers are very glad to