CHAPTER XXIV. Functions and Instincts. Mammalians. WE are now arrived at the last and highest Class of the Animal Kingdom, to which man himself belongs, and of which he forms the summit: but though he may be said to belong to it in some respects, in others he stands aloof from it, as an insulated animal, and one exalted far above it, being created rather to govern its members, than to be the associate of the highest of them. This Class includes many animals which are of the greatest utility to man, and without which he could scarcely exist, at least not in comfort; and others again that attack him and his property: and though the fear of him, in some degree, still remains upon them, also often excite that passion in his breast. But he, of all animals, is the only one, that by the exercise of his reasoning powers and faculties, can arm himself with factitious weapons, enabling him to cope with the superior strength, the fierceness, claws, and teeth of the tiger or the lion, and to lay them dead at his feet when in the very act of springing upon him. The animals of this Class, that are terrestrial, are all quadru peds, and are mostly covered with fur or hair, longer or shorter, though in some these hairs becomes quills, as in the porcupine, or spines, as in the hedgehog; others, like the serpents and lizards, are protected by scales, as the Manis; and some are incased in a hard coat of armour, often consisting of pieces so united as to form a kind of mosaic, as the armadillo, the Chlamyphorus, and probably the Megatherium. In the aquatic Mainmalians the legs are, more or less, converted into fins, or means of natation. The whole body constituting the Class, though sometimes varying in the manner, are all distinguished by giving suck to their young, on which 1 Τετράποδα της γης. 3 See above, pp. 256, 265, 2 PLATE XVII. account they were denominated, by the Swedish naturalist Mammalians.1 The situation and number of the, usually protuberant, organs that yield the milk, vary in different tribes and genera. The Creator has distributed them according to the circumstances of each kind. Physiologists divide them into pectoral, or those on the chest; abdominal, or those on the abdomen; and inguinal, or those on the groin. In the human race, the Quadrumanes, and the bats, and some others, these organs are placed between the arms. For an erect animal like man, it is evident that this situation for the paps was the only convenient one for suckling an infant, either when sitting or standing; the monkey tribes also, which are always moving about upon trees, and among the branches, could not have exercised this maternal function, had their lactescent organs been placed lower; and the bats, which carry and suckle their young during flight, required that their nipples should be similarly placed, to enable them to keep fast hold. All the species of the above tribes have only a pair of the organs in question, with the exception of the lory, or sloth-ape, so called from the excessive slowness of its movements, which has four, two of which Cuvier places in his abdominal column, under the name of epigastric. The animals which produce more than two at a birth, as might be expected, have a proportionable number of nipples differently distributed. Thus the cat has four pectoral, and four abdominal. The ten nipples of the swine are all abdominal, and those of the other Pachyderms, with the exception of the elephant, which has only two pectoral nipples, are similarly situated. The jerboas has both pectoral and inguinal ones, while the lemming has all three kinds; the Ruminants, Solipeds, Amphibians, Carnivorous Cetaceans, have only inguinal dugs, with from two to five nipples. This situation is evidently best suited for suckling their limited number of young ones. Amongst the Marsupians, whose young, immediately upon their birth, pass into a second matrix as it were, almost the entire skin of the abdomen forms a pocket, inclosing the lactescent organs; those of the opossum are arranged, in Cuvier's table, in the inguinal column; but in the Kanguroo, which has four, they appear rather to be abdominal. These variations in the position and number of the organs furnishing 1 Cuvier calls them Mammifera, but there seems no reasen for altering the original term. 2 Stenops. 3 Dipus Sagitta. 4 Lemmus. the sole food of the animals of the present Class in their state of infancy, were evidently planned and formed by the hand of a being supreme in Wisdom, Power,and Goodness, who adapted every organ to the circumstances in which it was his will to place the diversified animals that compose it, and to their general structure. To those which produce not more than two at a birth, only two organs for suction were usually given, placed, according to the wants of the animal, either between the anterior or posterior extremities, in which latter case the posture was never erect; but where he decreed an animal should produce a more numerous progeny, he planted them in greater numbers, and so distributed them that all belonging to the same litter could suck at the same time. In the case of the Kanguroo the members of two litters are sometimes sucking at the same time, which accounts for their having four nipples, a fact which shows how accurately every thing has been foreseen, weighed, and numbered, by a Provident Intellect. In the whole animal kingdom, except amongst the Mammalians, there is no instance of the young being supported by their parents with nutriment derived from themselves, nothing, therefore, affords a clearer character for a definition of the Class than this most interesting one: the Birds, indeed-with the exception of pigeons which feed their nestlings from their cropas well as the bees, and several other Hymenopterous insects, provide their progeny with food which they collect for them themselves; but the great majority of invertebrated animals, confine their care for the n, to placing their eggs in a situation in which, when hatched, they would meet with their appropriate food, and this appears to be all that is generally done. priate and classes and the by the two first classes of Vertebrates, the Fishes, and the Reptiles. MAMMALIA. (Beasts.) Animal vertebrated, ovoviviparous, or viviparous. Extremities ambulatory, or natatory; in a few organized for flight. Integument pilose; sometimes spinose, or armed with hard scales or plates; and sometimes naked. Young not hatched by incubation, but when first extruded from the matrix, receiving their nutriment by suction, till they can support themselves. Circulation double. Blood red, warm. Cuvier seems to have laboured under some difficulty with regard to the Classification of Mammalians, and to have regarded the Marsupians and Monotrèmes as forming a distinct Class, divisible, for the most part, into Orders analogous to those into which the Class of common Quadrupeds is divisible.1 Subsequent observations have proved the general correctness of this idea. Mr. Owen observes to me, in a letter, "Dissections of most of the genera of Marsupians have tended to confirm in my mind the propriety of establishing them as a distinct and parallel group, beginning with the Monotremes, which I believe to lead from Reptiles, not birds. A general simplicity in the structure of the brain; a less perfect condition of the vocal organs; some peculiar dispositions of the great veins and arteries, as the presence of two superior vena cava, and the absence of an inferior mesenteric artery, are among the circumstances in which they, the Marsupians and Monotrèmes differ from the true viviparous Mammalians, and agree with the oviparous Vertebrates. Recent opportunities of examining the impregnated uterus of the Kanguroo and Ornithorhynchus have almost determined that they are both ovoviviparous." Under these impressions, confirmed and illustrated by the observations of so able a comparative anatomist, I shall consider the Class of Mammalians as divisible into two Sub-classes, viz. Ovoviviparous Mammalians, and Viviparous Mammalians. It may be here observed, with regard to the state of forwardness in which the different tribes of Mammalians leave the matrix, a considerable variation takes place, some requiring a longer time than others, before they can be considered as at all independent of maternal care and protection. The young of the Ruminants, Pachyderms, and Solipeds, come into the world with the organs of the senses and of locomotion, in a state to be used immediately; they can see with their eyes, and hear with their ears, and walk with their legs, as soon as they are born; whereas the Predaceans and several others, when first born are blind, and unable to walk, and do not attain to the full use of their eyes and legs till a considerable time after birth. In man, though the infant is born seeing, yet a much longer period and the instruction of the mother or nurse, are required before it can walk. In the first case here noticed, that of the Ruminants and Pachyderms, the young animal requires less care from the mother. She has little to do besides suckling, and watching it in order to protect it if danger threatens. But, in the second 1 Règn. An. i. 174. case, she must prepare a kind of nest, not exposed to the light, and removed from observation, in which she can attend to her young unmolested, till they can see and move about upon their legs. Every one knows how attentive feline animals are to these circumstances, and the Rodents often excavate burrows in which they bring forth and suckle their young. The Marsupian Mammalians probably are exposed to external circumstances, which render it necessary that they should have a kind of nidus formed of the skin of their own body, to receive their young when they leave the matrix, at which period they seem to be in a more helpless state than any of the animals last alluded to.1 From this statement we see that the graminivorous and omnivorous animals, whose food is always at hand, come into the world the best prepared for action; while the carnivorous ones, and those that must, if I may so speak, procure their daily bread by the sweat of their brows, require to be in some degree educated for their function, before they can duly exercise it. In the instance of the Ornithorhynchus, a burrow, seems to supply the place of the marsupial pouch, which indicates some approach to many of the Rodents. Sub-class 1.-Ovoviviparous Mammalians. Chorion, or external membrane of the egg not rendered vascular by the extension of the foetal vessels into it. Embryo not adhering to the uterus. Only one passage out of the body. Marsupial bones in all. This Sub-class is divided into two Orders, Monotremes, and Marsupians. Order 1.-Monotremes (Ornithorhynchus; Echidna.) No marsupial pouch. Coracoid bones extended to the sternum. Young suckled from a mammary orifice: brought up in burrows. Animal predaceous. Order 2.-Marsupians (Wombat; Koala; Kanguroo; Phalangist; Flying and Common Opossum, &c.) A marsupial pouch receiving the young after birth, in which they are suckled by means of nipples. Animal herbivorous, predaceous, or carnivorous. Sub-class 2.-Viviparous Mammalians. Chorion, or external membrane of the egg rendered vascular by the extension of the foetal vessels into it. Embryo adhering to the uterus. 1 Owen in Philos. Tr. 1834. 344. 3 Owen ubi, supr. 564. 2 See above, p. 327. |
