CHAPTER IX. (W.) REPRODUCTION AND TRANSFORMATION. THE production of one living thing from another, and its first Maing into existence, is a mystery into the intimate nature of ich we cannot hope to penetrate. We are well acquainted ..ith some of the details of the process, but the mode in which the principle of life is transmitted from one being to another, and by which it is able to convert common matter into a living tissue, eludes our observation. The medium of this transmission in the case of the plant is a seed, and in the animal an egg. The nature and purpose of these two bodies is essentially similar. Each is the germ of the new creation. The circumstances in which they differ have been before pointed out, but those in which they resemble each other are quite as striking. The egg may be developed and nourished within the body of the mother, in which case the young are born alive; but in by far the larger part of the animal kingdom it is thrown out by the parent, and goes through a subsequent process, called incubation. A certain degree of heat is necessary to this, as is shown by the fact that some degree of cold will arrest it.* The eggs of many insects are laid in the fall, but remain dormant through the winter, the heat of spring or summer being necessary to their development. Among birds, a more equal and constant as well as a higher degree of warmth is necessary, and this is usually supplied by the body of the mother. In hot climates the external * In birds, a heat nearly approaching that of the parent animal is required. In reptiles, fishes, insects, &c., the temperature of the medium in which they live at the breeding season is sufficient. How low the temperature may fall without arresting the process in the lower classes is not certain. In the arctic regions, during the summer, insects appear in great numbers when the thermometer rises to 45° in the daytime, although during some part of every day it falls many degrees below the freezing point. Probably, therefore, the embryo is frozen during some part of every day during the whole process of incuoation; but it is not likely that any active progress ever takes place below 320, if so low as this. heat is sometimes sufficient, and the parent trusts partially' to this, as is the case with the ostrich. The eggs of the warm-blooded animals are very tender, and their vitality is destroyed by the cold of winter, whilst those of many others exhibit great tenacity of life, and survive not only the influence of cold, but also of extreme heat. They seem even capable of surviving the process of digestion, of entering into the blood and composition of the tissues, and of becoming afterwards developed, either in the body of the living animal or after its death. Captain Franklin says, that on the shores of the Polar Seas (lat. 69° 30', long. 140° 50') when the thermometer rose to 45° they were tormented with mosquitos, and that they retired when it fell below this. The immediate activity of these and similar insects upon the beginning of warm weather, in regions where the temperature falls often to 50° and 60° below zero, and is below the freezing point during some portion of almost every day in the year, illustrates strongly the preservative powers of the vital principle both in the animals themselves and in their eggs or larvæ. They must of course exist in a frozen state at least eight or nine months, and many may, by being inclosed in masses of ice, escape the influence of the heat of summer, and thus remain congealed year after year. If one year in this condition does not destroy their vitality, there is no reason to suppose that a longer period will; and thus it is not impossible they may remain for centuries in a dormant state, and at length, if accidentally brought under the influence of a summer's sun, be roused to life and activity. Moisture is another condition necessary to the activity of animal life. The vitality of the eggs of the higher animals and of the animals themselves is destroyed by drying. It is not so with the lower, nor with the seeds of plants, nor even with some plants themselves. The seeds of the Egyptian wheat have been found in mummies 3000 years old, and have germinated under the usual conditions. The snail has been restored to life after being perfectly dried; and many of the Radiata, especially the Infusoria, are capable of enduring the same state for an unlimited time.* *This has been lately called in question, and extensive observations have The influence of atmospheric air is also necessary to the development and activity of life. The seeds of many plants will remain dormant for years, if buried deeply in the earth, — probably for an indefinite period. Some animals are well known to retain life under the same condition. Frogs and toads have been found imbedded in stones or at a great depth in the earth, where they must have remained for ages; and have resumed their functions as soon as extricated from their captivity. This is probably equally true of animals lower in the scale, who have a much greater tenacity of life; and still more, of their eggs and larvæ. In these ways the ice of the polar regions and the materials of our globe may be full of animals or their embryos in this latent state, which only require to be exposed to heat, air, and moisture to assume all their appropriate functions. It is a curious and interesting consideration, that in this way an animal whose active state is usually limited to a single season may have its existence protracted almost indefinitely. Still its period of positive activity is not probably extended, since, in the passive state to which it is reduced, there is a complete suspension of all its functions, and there is consequently no exhaustion of the powers by which life is maintained. The instinct of animals is in no way more remarkably exhibited than in the provision they make for the well-being and support of their young, and this more among the lower than the higher. This instinct varies with their nature, and with the character of the offspring to be produced. In the common hen, it is at first an impulse which seems merely the result of a physical sensation, inducing her, after laying her eggs, to sit upon them patiently till the chick breaks the shell and utters its first cry. The moment this cry is heard it awakens a new sentiment, the maternal, the most tender and beautiful in nature. This impels her to leave her nest and search for food, and then for the first time she utters the peculiar call which her young so well understand. Till this been made by competent naturalists with a view to determine it. Still, although doubt has been thrown upon the capacity of animals to survive the perfect and entire exclusion of water from their texture, it seems most probable that the retention of a very minute quantity is sufficient to prevent their destruction. moment she appears to have no conception of the nature of the office in which she is engaged. She sits with the same assiduity upon an artificial egg, upon a stone, or upon an empty nest. It is not at any particular period that the maternal instinct is awakened, for if her eggs are removed or become addled, she remains brooding over her nest with the same untiring perseverance, for some weeks after her young should have made their appearance. In insects, the blindness and at the same time the precision of this instinct is more strikingly exhibited. In some species the butterfly which lays the egg feeds upon flowers, whilst the worm that proceeds from it is carnivorous. But the parent places within its reach the food which its offspring needs, and not that upon which it is itself nourished. A species of beetle, called, from its peculiar habits, the burying beetle, deposits its eggs in the dead bodies of animals which it afterwards buries, in order that its young when they leave the egg may have a supply of food. Their industry in accomplishing this is most remarkable. In the course of fifty days, four of them were observed to bury no less than twelve bodies, among which were two frogs and a linnet. Even living animals do not escape the same fate. In the Mauritius, a traveller informs us that there is a large fly, something like the cantharides, who selects the cockroach as his victim, and fills its body with his eggs. A species of ichneumon deposits his progeny in the body of a caterpillar. The little grubs, when hatched, maintain themselves by sucking the juices and devouring the textures of the unfortunate victim, but carefully avoid all vital parts, so that he continues to live and feed as usual till he is about to pass into the chrysalis state. Then the little ichneu mons leave him. He presents the appearance of an almost empty skin, and dies a caterpillar. In this case it is stated that the egg is deposited, not in any part proper to the caterpillar itself, but in the embryo butterfly already formed within, whose life is independent, and whose destruction, therefore, inflicts no injury upon the caterpillar. The instinct of maternity, when in a state of activity, often produces, especially in the higher animals, a great change of - always are devoted character. The whole life and energies of the parent, of the female and in some cases of the male also, to providing for and defending their young. The timid become bold, the weak powerful; whilst the courageous and strong become doubly ferocious and violent. The eagle will not hesitate to attack any animal, even man, that assails her nest, whilst every one knows how fearless and devoted is even the common fowl when its brood is in danger.* If we lift up a stone beneath which is a colony of ants, each one is seen at once to seize an embryo in its arms and scramble off to deposit it in a place of safety. The common earwig watches over its progeny as sedulously as the hen; broods over them, leads them forth, and collects them when scattered. The spider will defend its bag of young ones to the last extremity, and suffer itself to be destroyed rather than part with it. Some moths strip the down from themselves, "to defend from the winter's cold the brood which the insect mother will never see." The poppy-bee digs a hole about three inches deep, in shape like a Florence flask, lines it with the bright petals of the poppy, partly fills it with a mixture of pollen and honey, and in this magazine of food deposits her egg. In short, the whole history of animated nature is filled with similar examples of the wonders which this instinct is capable of performing. . But although so powerful in degree, this instinct is far from being discriminating or uniform in its operation. Some animals, as the hog and the rabbit, often devour their young. The com mon fowl, though so fierce in defence of her brood, is regardless of their safety in many other points, and will often carelessly trample them to death in her nest, or injure them by violence while scratching for food. She does not recognize the distinction "In the middle of June, 1821," says Dr. Richardson, "a pair of these birds [eagles] attacked me as I was climbing in the vicinity of their nest. They flew in circles uttering loud and harsh screams, and alternately stooping with such velocity that their motion through the air produced a loud rushing noise. They struck their claws within an inch or two of my head; and I endeavored, by keeping the barrel of my gun close to my cheek and suddenly elevating the muzzle when they were in the act of striking, to ascertain whether they had the power of instantaneously changing the direction of their rapid course, and found that they invariably rose above the obstacle, with the quickaess of thought, showing equal acuteness of vision and power of motion." |