Two agencies of the most opposite, character have apparently been, at all times, acting on the crust of the earth to change its form, or add to the surface of dry land—the volcano and the insect!—the one the most sudden and violent imaginable, producing in a short time the most astonishing effects; the other gradual, silent, and imperceptible, yet leaving the most stupendous monuments of its activity. The volcano has thrown up a mountain in a single night; there is an instance, too, on record, where a mountain has quite as suddenly disappeared, destroying itself in its own violent combustion, and breaking up with repeated and terrific explosions. On the other hand, besides what has been long known of the works of the coral insect, the microscope has revealed to us that huge cliffs have been constructed of the minute fossil shells of animalcule. These creatures, abstracting from the water, or the air, or both, the minute particles of vegetable or other matter they hold in solution, first frame of them their own siliceous shells, and then deposit these shells by myriads, so as ultimately to construct enormous solid mounds out of imperceptible and fluent particles.
Astonishing, indeed, is the new world of animals invisible to the naked eye, which science has lately detected.
"Professor Ehrenberg," says Mrs Somerville, "has discovered a new world of creatures in the infusoria, so minute that they are invisible to the naked eye. He found them in fog, rain, and snow, in the ocean and stagnant water, in animal and vegetable juices, in volcanic ashes and pumice, in opal, in the dusty air that sometimes falls on the ocean; and he detected eighteen species twenty feet below the surface of the ground in peat earth, which was full of microscopic live animals: they exist in ice, and are not killed by boiling water. This lowest order of animal life is much more abundant than any other, and new species are found every day. Magnified, some of them seem to consist of a transparent vesicle, and some have a tail; they move with great alacrity, and show intelligence by avoiding obstacles in their course: others have siliceous shells. Language, and even imagination, fails in the attempt to describe the inconceivable myriads of these invisible inhabitants of the ocean, the air, and the earth."
With every great change, however brought about, in the surface of the earth, and the climate of its several regions, it appears that, either by the direct agency of the Omnipotent Creator, or through the intermediate operations of laws which are at present profound secrets to us, a corresponding change takes place in the forms of animal life, and in the whole vegetable kingdom. Modern science presents no subject to us of more interest than this, and none apparently so inscrutable. Nor does the examination of the globe, as it exists before us at this moment, with its various floras and faunas, at all assist us in forming any conception of the law by which the geological series (if we may so term it) of animal life, has been regulated, for the distribution of the several animals over the several countries and climates of the world follows no rule that one can detect. Of course, no animal can exist where provision has not been made for its subsistence, but the provision has been made with the same abundance in two countries, and in the one the animal is found, and the other not. We should ask in vain why the horse was found a native of the deserts of Tartary, and why it was originally unknown to the plains of America? Nor can any cause be detected for the difference between the congeners, a representative species of one continent or island, and those of another. And not only have the larger animals an arbitrary territory marked out to them by nature, but birds, and even insects, are separated and grouped together in the same unaccountable manner. The chapters which Mrs Somerville has devoted to this subject will be read, especially by those to whom the topic is new, with extreme interest. They are enlightened and judicious.
It is a natural supposition to make, that, in the series of animals which at great geological periods have been introduced upon the earth, there has been a progression, so that each new form of animal life has been, in some marked manner, superior to that which is substituted. The comparative anatomist has not sanctioned this opinion; he tells us that he finds the same "high organisation" in the fossil saurians of a bygone world, as in the lions and leopards of the present day. But we would observe that the presence of this "high organisation" is not sufficient to determine the question. We should be surprised, indeed, if any creature were to be found whose structure was not perfectly adapted to the mode of life it was destined to lead. But it is permissible to compare one animal with another in its whole nature, and the character of its existence. The pig has the same high organisation as the dog, yet we should certainly prefer the one animal to the other; we should say that it was calculated for a happier life. We cannot suppose that a bird is not a more joyous creature than the worm or the snail. The adaptation of the whole form and structure to a pleasurable existence, and not what is termed high organisation, is that which we must regard, in estimating the superiority of one animal to another. Now, in this respect, there surely has been a progression from the earliest epochs. The crocodile and the tortoise are, amongst the animals which now exist, those which most resemble some of the more remarkable of the extinct genera. They are as perfectly adapted, no doubt, as any other creature, to their peculiar mode of being; but that mode of being is not an enviable one. The long stiff unwieldy body of the one, and the slow movement, with the oppressive carcase, of the other, are not consistent with vivid animal enjoyment. The crocodile, accordingly, lies motionless for hours together—waits for its prey—and slumbers gorged with food. And for the tortoise, it appears to lead a life as near to perpetual torpor as may be. Pass through a museum, and note those huger animals, the elephant and the rhinoceros, the seal or walrus, all those which most remind us of the gigantic creatures of the antediluvian world, and compare them with the horse, the deer, the dog, the antelope. Surely the latter present to us a type of animal life superior to the former—superior, inasmuch as the latter are altogether calculated for a more vivacious, sprightly, and happy existence. We must not venture to remark on their greater comparative beauty, for we shall be told that this is a matter for our own peculiar taste. We should not be contented to be so easily silenced on this head, but we should require far more space than we have now at our disposal to defend our æsthetic notions.
We have found ourselves imperceptibly conducted from the inanimate to the animate creation; we shall proceed, therefore, with the same topic, in the few farther extracts we shall be able to make from the work before us. Indeed, with so vast a subject, and so brief a space, it would be idle to affect any great precision in the arrangement of our topics; enough if they follow without abruptness, and are linked together by natural associations of thought.
"Three hundred thousand insects are known!" and every day, we were almost going to add, increases the number. They abound, as may be expected, in equatorial regions, and decrease towards the poles. "The location of insects depends upon that of the plants which yield their food; and as almost each plant is peopled with inhabitants peculiar to itself, insects are distributed over the earth in the same manner as vegetables; the groups, consequently, are often confined within narrow limits, and it is extraordinary that, notwithstanding their powers of locomotion, they often remain within a particular compass, though the plant, and all other circumstances in their immediate vicinity, appear equally favourable for their habitation."
Mountain-chains, Mrs Somerville observes, are a complete barrier to insects; they differ even in the two sides of the Col de Tende in the Alps, and they are limited in the choice of their food. If a plant is taken to a country where it has no congeners, it will be safe from the insects of that country; but if it has congeners, the insect inhabitants will soon find the way to it. Our cabbages and carrots, when transplanted to Cayenne, were not injured by the insects of that country; and the tulip tree, and other magnolias brought here, are not molested by our insects.
The insect is a race, or order, of creatures not friendly to man, or any of the larger animals.
"The mosquito and culex are spread over the world more generally than any other tribe; they are the torment of men and animals from the poles to the equator, by night and by day; the species are numerous, and their location partial.... Of all places on earth, the Orinoco, and other great rivers of tropical America, are the most obnoxious to this plague. The account given by Baron Humboldt is really fearful; at no season of the year, at no hour of the day or night, can rest be found; whole districts in the Upper Orinoco are deserted on account of these insects. Different species follow one another with such precision, that the time of day or night may be known accurately from their humming noise, and from the different sensations of pain which the different poisons produce. The only respite is the interval of a few minutes between the departure of one gang and the arrival of their successors, for the species do not mix. On some parts of the Orinoco, the air is one dense cloud of poisonous insects to the height of twenty feet."