ON THE EVIDENCES OF UNITY AND DESIGN DISPLAYED IN THE ORGANIZATION OF ANIMALS.-No. II.

BY A LECTURER ON PHYSIOLOGY.

In our former paper some account was given of feathers and scales: we propose now to consider the external coverings of the highest class of animals, mammalia, so called on account of their possessing mamma or milk glands, affording nourishment for their new-born offspring.

The coverings of mammals comprise hair, fur, wool, bristles, quills, horn, bone; these we shall briefly describe. Hair is more particularly provided for animals which inhabit warm and temperate climates, whilst fur and wool are invariably met with in creatures living in the colder regions, although they are occasionally seen in the temperate and even tropical parts of the earth.

If a single hair be examined whilst it is lodged in the skin, it is found that the enlarged part, called the root, rests upon a highly-organized structure, the bud or papilla, consisting of numerous cells, which secrete and form the hair. The whole structure is surrounded by very vascular membranes, the arteries of which supply the papilla, but do not themselves nourish the hair. The curious fact has been noticed, that the hairs will continue to grow for some time after death; of this there can be no doubt, as we have ourselves repeatedly seen that the beard has grown in the dead body. Nor is it difficult to understand the cause of this phenomenon, since it is now distinctly ascertained that the process of secretion, upon which all growth depends, is effected not by the blood vessels, which was the opinion formerly received, but by the important organs, called nudeated cells; in the case before us, a certain amount of nutritious matter having been deposited in the cells of the papilla, and the organic life surviving for some time the destruction of the animal functions and the circulation, growth to a certain extent may still continue.

Every form of hair, fur, bristles, &c., grows in the manner described; and the activity of the process may be estimated by making a puncture in the root of the finger-nail, an analogous structure, and colouring it with lunar caustic; in the course of two or three months the mark will have advanced to the free end of the nail. It is almost needless to add that the hairs will be readily reproduced after extraction, provided the formative organ, the papilla, is not destroyed.

The quality of hair varies remarkably in the several classes of animals, and particularly according to climate, as we see in comparing, for example, dogs brought from different countries; those of "cold climates," as Dr. Pritchard remarks, "have generally two kinds of hair,—a fine woolly hair, close to the skin, and a long silky hair. In tropical climates the former lessens and finally disappears altogether, and the same thing happens in our dwellings which afford shelter from inclement temperatures." different in these respects are the Polar and Iceland dogs from the Italian greyhound; the former warm and rejoicing in our severest winters, the latter shivering and trembling even in the summer's sun of these northern regions.

How

That there is a perfect adaptation of this defensive covering to the degree of exposure, becomes, however, more apparent when such animals as the seal, the otter, and the ornithorhynchus, or duck-billed animal of New Holland, are examined. In all of these there are the two kinds of hair above mentioned, or rather an external covering of hair, and a thick close set layer of fur. In these creatures, as in all other mammalia, an oily secretion is derived from a vast number of glands provided expressly for the purpose; and as a pair of these small bodies, technically called sebaceous glands, is placed within the sheath of the skin which lodges each individual hair, an ample supply is poured out, and the water, as in the case of the aquatic bird and fish, is thus repelled and the animal kept dry.

It is not often that an opportunity is afforded of observing the habits of these creatures; but doubtless they are as careful in arranging and keeping their fur in order, as birds are with respect to their plumage. Mr. G. Bennett, who has given the most perfect account of the ornithorhynchus, whilst in its native abodes, states, that one of these animals which he kept some time in his possession, after feeding would lie partly in and partly out of the water, combing and cleaning its coat with the claws of the hind feet, and that after this process, which occupied a considerable time, its sleek and glossy appearance was greatly improved. We have observed a seal in the Zoological Gardens performing the same operation with the fore feet. The kangaroo has on the hind foot two small toes, which hang, as it were, from the skin, and have evidently no relation to support or locomotion; they have, however, nails, which, according to Mr. Waterhouse, are used by the animal as a kind of comb to cleanse and arrange its coat.

All these coverings act as a defence against the effects of cold, by entangling a large quantity of hair, which, as we explained in a former paper, being a bad conductor of caloric, tends to retain the animal heat; and therefore the more fine and abundant the wool or fur, the more effectual will be the protection afforded. The dealers in these articles are quite aware of the differences in this respect; and their lady customers have also found out by experience that minx, although presenting as to colour, &c., the semblance of sable, has not the valued qualities of that skin. A friend coming north of the Tweed, assures us that no stockings are so warm as those made of the Shetland wool, and the observation is probably well founded.

Some of the most interesting circumstances connected with the coverings of mammiferous animals, relate to several extinct genera of the edentata and pachydermata. To the latter belong the elephant and rhinoceros, which, in the existing creation, having for their habitation the sultry climates of Africa and Asia, do not require, and therefore are not furnished with hair, with the exception of a few scattered bristles. But geological researches, among the many other interesting facts they have disclosed, show that at an earlier epoch both the above genera were fitted to live in colder climates. Thus, for example, bones and tusks of the fossil elephant or mammoth are found in such abundance and perfection in some parts of Siberia, and on the shores of the Frozen Ocean, that the latter constitute an article of commerce. But what is more to the point, there was discovered, in 1799, by a Tungersian fisherman, the body of an enormous animal imbedded in a block of ice, in which it had been preserved by a kind of embalment during unknown ages. When more completely disengaged from its frozen bed, it proved to be a colossal elephant of a peculiar

and now extinct species, and so effectively defended from decomposition, that the flesh remained, and was devoured by bears, wolves, foxes, and other wild animals; the skin also remained, and was covered with a coat of thick hair. This consisted of a very thick kind of wool, one inch and half long, next the skin, interspersed with some bristles about three inches long, and others of from twelve to eighteen inches in length; the surface was nearly black, whilst towards the skin the colour was reddish-brown, resembling in part the camel. We can picture to ourselves the strange appearance which a creature of this gigantic size (it was nine feet four inches high, and sixteen feet four inches long,) must have presented with its shaggy coat and mane.

The carcass of a two-horned rhinoceros (thus allied to R. Africanus) has also been drawn from the ice in Siberia, and which, like the elephas primigenius or mammoth, was covered with a thick fur. In these two instances we have a striking illustration of the adaptation displayed in animal organization according to the variation of external circumstances.

It has been stated, in the commencement of this paper, that some mammals have a covering of bone; they are the armadillos and their extinct congener, the glyptodon. These remarkable animals, placed in the zoological scale in the order edentata, between the sloths and the ant-eaters, differ from all other mammalia by having a strong kind of buckler or armour in place of hair and fur. It is divided into three principal portions, covering the head, shoulders, and rump; but it also presents multitudinous subdivisions, varying in the several species, the pieces being usually disposed in parallel concentric rings, and thus having a resemblance to plate armour. The armadillos are active, inoffensive animals, feeding upon fruits, roots, worms, insects, and carrion, the largest among them (dasypus gigas, Cuvier,) measuring from the nose to the end of the tail about four feet eight inches.

The most interesting point in the economy of these creatures is, a peculiarity in the construction of the vertebral column, adapted evidently to the support of the weighty armour. Professor Owen has shown that there are two additional processes or portions of bone in the armadillos which are not found in any other mammal, and which, as will be seen on referring to the accompanying wood-cut, act like the "struts or braces" which in the frame-work of the roof assist the "king post" to support the rafters.

A single vertebra of the Armadillo, showing the two peculiar lateral processes of bone, supporting the armour.

The distinguished zoologist named above has, in a very masterly investigation into the affinities of the enormous extinct animals, the megatherium, mylodon, and glyptodon, satisfactorily proved that the two former were hair-clad mammals of the edentate order, allied to the sloths; whilst the latter has been shown to be a gigantic armadillo, both by the discovery of almost the entire armour, and by the construction of the vertebral column.

Glyptodon Clavipes, OWEN. The drawing is copied from the Descriptive and Illustrated Catalogue of the Fossil Organic Remains, contained in the Museum of the Royal College of Surgeons, 1845.

We have appended a drawing of the glyptodon clavipes, Owen, and also of one of the caudal vertebræ, in which the development noticed in the armadillo, is carried to the fullest extent; in fact, the several processes almost resemble the spokes of a carriage-wheel supporting the tire. Some idea of the magnitude of these extinct edentate mammifers may be formed from the fact that the megatherium was eighteen feet in length, and seven feet high; the mylodon, eleven feet long; whilst the carapace, or armour covering the trunk of the glyptodon, exclusive of the head, neck, and tail, equals five feet seven inches in length.

THOUGHTS ON THINKING.

BY THE AUTHOR OF "MENTAL CULTURE."

MAN is a thinking being. It is this which dignifies and elevates him, and assigns to him the lordship over the irrational world. Some have asserted that the soul of man always thinks, and that actual thinking is as inseparable from the soul as extension is from the body. Be this as it may, the mind, in our waking moments, is ever thinking. It is, in this respect,

as restless as the ocean's waves-no calm, however deep, stays their rippling. But, of the ten thousand thoughts which hourly pass through the mind, how few are worth retaining; the majority of them rise not higher than the things of common life-they range only within the narrow limits of a secular world, or in the regions of fancy, whilst the few only surmount the skies to dwell upon the objects of faith.

Nothing, however, shows more strikingly the moral degeneracy of man than this; for surely, if he has inducements to think at all, in the highest sense of that word, he has them to think on revealed truth. His own mysterious being, with its restless passions, and quenchless hopes-the world in which he moves, so full of God's beauteous works,—the frailty of his body-the brevity of his life, and the transitory nature of earth's scenes, powerfully urge to religious thoughtfulness. How strange and humiliating is the fact that man should be so unconcerned because so thoughtless about a restoration from his moral degeneracy, though by nature, by Providence, and by revelation, is he reminded, in various ways, what he is, where he is, and whither he is going. It is a futile and incorrect notion that he is taught to be religious only from the Bible. What are the changes and revolutions of empires-what the rise and fall of kingdoms-what the devastation by storm and tempest-what the mortality by the pestilence which walketh in darkness and at noon-day, but the Almighty, in his providence, speaking to man, and urging him to religious thoughtfulness! Nature is but a reflection of her Creator. All her glorious works proclaim his wisdom and his goodness-his power and his skill. She presents her lessons, and man does well to read them; for

"Stars teach as well as shine."

There is no language nor speech where nature doth not utter her voice. The "Great Teacher" of man, in the days of his sojourn on earth, taught the sublimest truths from the flower of the field-the birds of the air, and the clouds of Heaven. The lily of the valley fixed his attention, and moved him to read to the world the lesson it conveyed. He saw God in every thing, and all creation in his ear spoke of God, and sang his praise.

He

Every thing will show a thoughtful mind, that man was intended to pursue a higher end than merely securing support for his animal existence, and to seek higher objects than what belong only to time and sense. was originally created god-like, and it is still the will of his Creator that he live for a god-like end. It is his privilege, as well as duty, to bend his thoughts and stretch out his affections towards the great things unseen, yet substantial and eternal, for "He builds too low who builds beneath the sky."

This truth is more clearly set forth and more firmly established in that moral revelation which God has made in the book, "writ with an immortal pen." It contains his will concerning man-it opens to him the future world, and tells him his duty in this-it lays open the wickedness of the human heart, and unmasks human nature-presents it in its true character, and points to the remedy of moral evil, and to the compassionate Restorer of a disordered and ruined world. It is the regulator of all conduct—the guide of every action-it is the light which shineth in a dark place—it is the high tower from the enemy-the solid rock in life's rough sea. In fine, it is the sure and unerring guide through the mists and mazes of earth to