"That natural affection, so connatural to all or most creatures toward their young, what an admirable, noble principle it is implanted in them by a wise Creator!"-DERHAM. the mammalia, not excepting those which come into the world blind and naked. The pouch answers as a description of second womb, in which the young animals are brought to maturity. 338. The young of all the animals of this order are remarkable for their imperfect development at the time of their birth. Even in the species without pouches (for some have a mere fold of the skin, scarcely visible) the young hang under the belly of the mother for a certain time; then they mount on her back, and twist their tails round hers to fix themselves. The young of the kaola, which has no tail, fixes itself on the parent's back, and fastens there with its hands. It is remarkable that, in the unpregnant animal, the pouch is closed, being glued, as it were, to the body of the parent by a peculiar secretion. As the pregnancy advances, this secretion becomes absorbed, and the folds of the pouch are set free, so that just at the time when the young within the body of the animal' are prepared to leave it, the pouch or nursery on the outside is fitted to receive them.* 339. Why are the young of these animals born in such a helpless condition? Because by far the greater number of the marsupial animals are either leapers or climbers; and this peculiar arrangement of the organs of gestation is evidently intended to enable the loins to have more powerful action than they could have if the body of the animal were encumbered with full-grown young. 340. It has not hitherto been noticed by naturalists (the Author believes) that the peculiar gestation of the marsupialia forms an intermediate design between the complete gestation of mammalia and the egg-laying capacity of birds. To animals of flight, the loaded womb, apart from any consideration of the number of the offspring, must be a serious impediment; they are, therefore, endowed with the power of excluding the ova and maturing their young apart from their own bodies. To animals that are terrestrial, and endowed with leaping powers, the encumbered womb must prove almost as great an impediment as to creatures of the air. The gestation, therefore, is imperfect, and is completed after the young has passed from the womb. It is also worthy of remark that as birds lay from two to fifteen or eighteen eggs, marsupial animals bear from one to twelve young ones. The pouch of the opossum is thus described by M. D'Argaza:-" The female has the whole length of the belly cleft or slit, and appearing like a person's waistcoat buttoned only at the top and bottom. This cavity the animal has the power of firmly closing. Within it are thirteen teats, extremely small, one in the centre and the rest ranged round it." The same authority speaks of one which he saw that had thirteen young ones. They had ceased to suck, and the pouch, since they were *Cuvier's "Règne Animal." "The trees, devouring caterpillars bare: Parched was the grass, and blighted was the corn."-DRYDEN. so much grown, was not large enough to contain them, but the mother carried them about fixed to her tail, legs, and body. The structure of these animals agrees with the contingencies under which they exist. They are subjected to considerable hardships, arising from the alternate parching and flooding of the countries in which they aboundcountries which are not adapted for the common mammalia in a state of nature-and accordingly we find that in New Holland, which may be considered the head quarters of marsupial animals, there are no native placental mammalia, and such are not very common in the other localities of these animals. New Holland, New Guinea, some of the other Islands of the Archipelago, South America, and the warmer part of North America, in the case of a single species only, are the localities of these animals, and it is not a little remarkable that not one of them has been hitherto found in Africa, though they occur on both sides of it.* 341. Why has the kanguroo such powerful posterior organs? Because the hind feet and the tail are employed as leaping organs, and also as weapons of defence. The leap is of very great length, and is accomplished by the action. of the tail, almost as much as by the legs. By the pliability of its spine and the flexibility of its posterior members, the animal can place itself preparatory to a bound so that, the lower bones of the leg being horizontal, the two superior bones shall be inclined to them at something less than a right angle, as shown in figures 1 and 2, representing the profile and the skeleton of the kanguroo; by which it will be seen how greatly the structure of the animal favours its principle of locomotion. *Partington's "Cyclopædia." "And on the playn of these valleys there were merualouse, 342. These proportions are reversed in quadrupeds of slow locomotive powers, of which the giraffe is one of the most remarkable examples. In this animal a great proportionate length is given to its fore-legs; so that, notwithstanding the length of its neck, it would be incapable of taking its food from the surface upon which it stands. Nature has, however, beneficially adapted the wants of the animal to its structure; and, while its head is elevated to a height of twenty feet above the ground, nourishment situated at a corresponding elevation is supplied in the foliage of the trees. 343. Why is the bounding movement of the kanguroo admirably adapted to the localities they inhabit? Because kanguroos inhabit a country where there are enormous tufts of the coarsest grass, growing on swamps or marshy ground, several feet in height, and at a considerable distance from each other; or else they frequent rocky or bushy ground. By means of the bound which they are enabled to execute they can clear from twelve to twenty feet in length and several feet in height, from one tuft of grass, or from one rock or bush, to another, and thus escape from their pursuers. 344. In kanguroos which have been bred and domesticated in this country, the fize and strength of the tail diminishes, and the animals more frequently use all four of their feet in running. This is a strong illustration of the care taken by a bencficent Providence of its creatures, in furnishing them with the means best "It was observed of this animal, that he leaped or bounded forward on two legs, instead of running upon four."-CAPT. COOK. dapted for their relative conditions and situations in the protection of themselves, end diminishing those means when they become no longer of the same importance them. 345. Why are the kanguroo's* head and fore paws so small? Because this conformation of the body is peculiarly adapted to its leaping habits; this form contributes to keep the body of the animal almost erect in the air, while the weight of the lower quarters brings it to the ground with precision, and in a natural position, prepared immediately to repeat the leap. 346. Why does the long-tailed belidens seldom descend to the ground? Because its structure, and especially the enormous length of its tail, is ill adapted for terrestrial habits; but it sometimes descends for the purpose of passing to a tree too distant to be reached by a spring. The tops of trees are traversed by this animal with as much ease as the most level ground is by such as are destined for terra firma. If chased or forced to flight, it ascends to the highest branch, and performs the most enormous leaps, sweeping from tree to tree. It has a membrane at its sides, which extends and forms a description of parachute, and which enables it to proceed to a considerable distance, always ascending a little at the extremity of the leap; by this ascent the animal is prevented from receiving the shock which it would otherwise sustain. 347. This fine little animal is common in all the bushes of New South Wales. In those vast forests, trees of one kind or another are perpetually flowering, and thus offer a never-failing supply of blossoms, upon which the little creature feeds; the flowers of the various kinds of gums, some of which are of great magnitude, are Le principal favourites.+ Commonly spelled "kangaroo," but more properly kanguroo. + Gould's "Mammals of Australia." "By dremes, by chirking of dores, or craking of houses, by gnawing of rattes, and swiche like manner of wretchednesse." CHAUCER. ORDER V.-RODENTIA. 348. Why are the animals of this order named rodents? Because of the peculiar formation of their teeth, and their habit of gnawing—the Latin verb rodo meaning to gnaw. 349. In the order Rodentia the front teeth cut with a sharp edge. We know that this is contrived in the tool of the carpenter, and we know that he must from time to time apply his chisel to the grindstone. The front teeth of the beaver, the porcupine, and the rat, are sharp, and yet not blunted by use; the bone of the tooth is the densest possible, consistent with the material; but, were the whole tooth of the same material, it would be ground down uniformly, and the original form of the instrument would be lost. Accordingly, a different substance, the enamel, which yields more slowly to friction than the bone, is, as it were, let in on the anterior surface of the tooth. The consequence is, that the enamel stands up sharp and exposed, so as to protect the bone of the tooth, and to give the surface which is worn down a certain shape, suited to act like nippers. The friction and the arrangement of the material of the tooth so far correspond, that the cutting form is preserved, however much the surface may be worn down. 350. Why are the jaws of rodents remarkably light? Because strength in the jaws is not requisite, but rather lightness, because the action is continued gnawing, or rubbing, and not powerful biting. This may be seen in the different ways in which a monkey and a squirrel go about to get at the kernel of a nut. The monkey takes it between his strong jaws, and cracks it at once by one lusty gripe, while the squirrel nibbles away till it makes a hole in the nut. 351. Why do squirrels convey food to their mouths with two paws while monkeys generally use but one? Because their fore-arms have but little motion in the elbow joints, and their two bones are often united. The paw, therefore, cannot turn, but has merely a hinge motion in this particular joint. Many of them, however, have tolerably perfect clavicles, and others have imperfect ones, so that they can bring the paw to the mouth without any turning of the elbow; but, as they cannot turn up the sole of the paw, they cannot bring any substance to the mouth except by holding it between the two paws sideways.* * Partington's "Cyclopædia." |