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lated by the same physical laws; and similar instruments are employed in effecting this infinite variety of purposes, by the all-wise and omnipotent Architect of Animated Creation."

The mechanical power here applied is the swelling of the belly of the muscle, and the consequent contraction of its tendons. This is easily understood; but what is totally unknown, and will probably continue to be unknown, is the substance or power, whatever it may be, which causes this swelling, whether voluntary or involuntary. It is different from any thing we are acquainted with, and we are unable to construct a machine, by any power of mechanism, which shall be endowed with the same principle. That principle, in short, is not mechanical, though it operates on a very refined piece of mechanism; and we can follow it no further. But there is no reason, arising from our ignorance of this unmechanical principle, which ought to throw any doubt upon the nature of the organization itself, or weaken the proof of intelligent contrivance which it affords. With the very same certainty as if we knew the origin of the motion, we can trace the artificial construction of the muscle for producing the necessary contraction, its skilful position for ef fecting a particular purpose, and the various combinations and adaptations of such instruments, so wonderfully uniting in a living body to form a perfect whole; and from all this we can derive a proof of design, which no sophistry can gainsay.

From such a mode of reasoning, we may discover both the advantages and disadvantages under which the physiologist labors, when he adduces the animal frame as a proof of Creative Wisdom; and Paley, after illustrating the subject much more at large, and arguing with his usual precision, comes justly to the following conclusions; first, that it is a mistake to suppose, that, in reasoning from the appearances of Nature, the imperfection of our knowledge proportionally affects the certainty of our conclusion, for in many cases it does not affect it at all; secondly, that the different parts of the animal frame may be classed and distributed according to the degree of exactness with

which we compare them with works of art; thirdly, that the mechanical parts of our frame, or those in which this comparison is most complete, and although constituting, probably, the coarsest portions of Nature's workmanship, are the most proper to be alleged as proofs and specimens of design.

FOURTH WEEK-TUESDAY.

REPRODUCTION AMONG THE LOWER ORDERS OF ANIMALS.

SPRING is peculiarly the season of reproduction; and the diversified means by which the various species of animals as well as plants are thus preserved, furnish one of the appropriate subjects of the season. The same character of similarity in the plan, and difference in the details, which belongs to the rest of the Creator's works, appears strikingly in this. A difference of sexes, which we have seen as one of the features in the reproduction of plants, is exhibited with not less uniformity in all the higher species of animated beings; in which last, however, this difference exists constantly in distinct individuals, and never, as frequently takes place among vegetables, in the same individual. But among the lowest orders of the animated creation, this uniformity seems to be departed from, and we have instances of reproduction altogether peculiar and anomalous. According to our plan of beginning at the lowest links of the scale, these shall form the subject of consideration in the present paper.

Fissiparous generation, as it is called, that is, the spontaneous division of the parent into two or more parts, is the simplest of all the modes of reproduction. Of such a mode, frequent instances occur among infusory animalcules. Many species of globular monads multiply in this way. At a certain period of their developement, a slight circular depression appears round the centre of these living balls, which, by degrees, becomes deeper, changing their form to the resemblance of an hourglass,

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till at last two globes are formed out of one, attached, like the Siamese Twins, by a single point. These twin existences are now seen swimming irregularly in the fluid which they inhabit, as if animated by two different wills. They struggle to get disunited, and for this purpose laboriously drag each other, first one way and then another, or, by a simultaneous movement, dart through the thickest crowd of the surrounding animalcules. The moment this slender filament is broken, they are observed moving away, without apparent recognition, and each beginning its own independent existence.

These globular animalcules are exceedingly small; and as the infusory tribes increase in size, they take a different shape, many of them being comparatively thick at one end, and tapering to a point at the other, somewhat in the form of a tadpole. Such of these, as follow the same law of reproduction with the monads we have mentioned, separate from each other lengthwise, forming the division by an incision beginning at the thicker end, and gradually becoming larger and larger, till, after a struggle similar to that of their globular congeners, they finally disunite at the hairlike extremity of the tail. Each animalcule thus formed, soon grows to the size which again determines a further spontaneous subdivision; and thus the same process goes on to an indefinite

extent.

"The most singular circumstance attending this mode of multiplication is, that it is impossible to pronounce which of the two new individuals, thus formed out of a single one, should be regarded as the parent, and which as the offspring, for they are both of equal size. Unless, therefore, we consider the separation of the parts of the parent animal to constitute the close of its individual existence, we must recognise an unbroken continuity in the vitality of the animal, thus transmitted from the original stem, throughout all succeeding generations. This, however, is one of those metaphysical subtilties, for which the subject of reproduction affords abundant scope.'

* Roget's Bridgewater Treatise, vol. ii., pp. 583-585.

In the vegetable kingdom, we have no instance of this kind of spontaneous division of an organized being into complete separate existences; but, by artificial means, this mode of reproduction may be effected. Thus a tree may be divided horizontally into slips, which may continue to grow, and may by and by produce a tree similar in all respects to that from which it originated. Even from a small fragment of a plant, under favorable circumstances, a complete plant may be formed, by roots shooting out from the one end, and a stem from the other. These facts show a peculiar species of reproductive power in the vegetable creation under the culture of man, but do not occur in the ordinary course of things.

Of this latter mode of multiplication, we have numerous examples in the lower departments of the animal kingdom. The hydra, or freshwater polype, is capable of indefinite multiplication by division, although this is not the natural mode of its reproduction. If it be cut asunder transversely the part containing the head soon supplies itself with a tail, and the detached tail shoots forth a new head, with a new set of tentacula [or feelers ;] and if the whole animal be divided into a great number of pieces, each separate fragment acquires, in a short time, all the parts which are wanting to render it an entire individual. The same phenomena are observed, and nearly to the same extent, in the Planaria. The Asteria, the Actinia, and some of the lower species of Annelida, are also capable of being multiplied by artificial divisions,-each segment having the power of producing others, and containing within itself a kind of separate vitality.

The

Something analogous to this, but by no means extending to the capability of reproducing a complete being, exists, in a certain degree, among the higher orders of animals, especially in the lower links of the chain. claws, the feet, the antennæ, and the entire limbs of some of the inferior species of these orders, are restored, when lost, by a fresh growth of the organs. The crab renews its limbs when torn off. If the head of a snail be amputated, the whole of that part of the animal, in

cluding its eyes and other organs of sense, will be reproduced. The tails of newts, and of some species of lizards, will grow again, if lost; and even the eyes of these animals, with all their complex apparatus of coats and humors, will, if removed, be replaced by the growth of new eyes. Among the highest class of all, too, similar powers exist, though much restricted. The principle which, in the human frame, closes a wound, repairs a broken bone, or alters the course of the blood when the ordinary channels are closed, is of the same nature, and forms a most beneficent provision.

The less perfect orders of that low class of animated nature, called Zoophytes, produce the species in a manner analogous to the buds of plants. At the earliest period in which the young of the hydra, for example, is visible, it appears like a small tubercle or bud rising from the surface of the parent. It grows in this situation, and remains attached for a considerable time, at first deriving its nourishment from the parent; then occasionally stretching forth its tentacula, and learning the art of catching and swallowing its natural prey. At length, the tube through which it received parental nourishment closes, the attaching filaments become more slender and break, and the young hydra moves away, and provides for its own sub

sistence.

Another plan of reproduction is that in which the germs are developed in the interior of the animal, assuming, in the first stages of animation, the form of the parent. In the volvox, a spherical revolving animalcule, of the infusory order, this mode is exemplified. The germs of this animal appear, by the aid of the microscope, in great numbers, in its interior, through its transparent covering; and while these are yet retained within the parent's body, other still minuter globules are developed within them, constituting a third generation. This progeny continues to swell till the parent bursts, and thus, in expiring, opens a passage for them to the element where they are, in their turn, to undergo the same destiny. In the case of the Actinia, the young, or gemmules, such productions are called, force their way through

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