Imatges de pàgina
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that every iota and tittle of an animal's structure, is with a view to some end important to it; and the Almighty Fabricator of the Universe and its inhabitants, when he formed and moulded, ex præjacente materia, the creatures of his hand, decreed that the sphere of locomotive and sentient beings should be drawn together by mutual attraction, and concatenated by possessing parts in common, though not always devoted to a common use; thus leading us gradually from one form to another, till we arrive at the highest and most distinguished of the visible creation; and instructing us by his works, as well as by his word, to cultivate peace and union, and to seek the good of the community to which we belong; and, as far as our influence goes, of the whole of His creation.

CHAPTER XVII.

Motive, locomotive, and prehensory Organs of Animals con

sidered.

The remarkable circumstances noticed in the last chapter,with regard to the legs of Crustaceans and Myriapods, and their employment in aid of manducation, sheds no small light upon the subject of locomotive organs in general, and their primary function; it will, therefore, not be out of place, if, in the present chapter, I consider those organs, as far as they are external, according to their several types, as exhibited in the entire sphere of animals; upon which, indeed, the due accomplishment of their various functions, and the exercise of their several instincts-which, in most of the succeeding classes, assume a new and more developed character-mainly depend. This is a wide field, but one full of interest, and which, studied as it deserves, conspicuously illustrates the higher attributes of the Deity.

We are placed in a world full of motion; of all motions, none fall more immediately under our notice than those of the various members of the animal kingdom; and the external organs by which they are effected attract every eye, both by their infinite diversity, and the adaptation of their individual structure to the occasions and wants of the animal in whom they are found, so that they may, in the best and safest manner, effect such changes of place as are necessary for their purposes.

Nutrition may be stated as the primary object of the motions and locomotions of the members of the animal kingdom in general. No sooner is the fœtus or embryo so separated from its parent stock, as not to imbibe its food from it, than it begins to employ instinctively its prehensory and motive organs in collecting it. And, whether we descend to the foot of the scale of animals, or mount to its summit, we shall find that their— Daily Bread-is the principal object that in every Class sets the members in motion.

The motive organs may be divided into two classes, those that are employed by an animal in locomotion, and those that are used for prehension; but as many of the locomotive organs are also prehensive, and prehension is often in aid of locomotion

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as in climbing and burrowing-it will not be easy to consider the motive organs separately with regard to these functions, I shall, therefore, consider them generally, according to certain types or kinds, under which they may be arranged, and which present themselves very obviously, when, with this view, we survey from base to summit, or rather from pole to pole, the entire sphere which constitutes the animal kingdom.

Generally speaking, in this survey, as well as in the peculiar motions of the various groups of animals, we have no trouble in ascertaining what are the external organs by which the Creator has enabled and instructed each animal to accomplish them; but there is one anomalous tribe, or, perhaps, it might be denominated Sub-kingdom, in one class of which, at least, this is not so obvious. I allude to Ehrenberg's Tribe of Plantanimals, particularly his first or polygastric Class, in which the organs of their various locomotions, enumerated in a former part of this work, remain unknown, and some, as those that have an oscillatory movement, one might almost suspect were moved by an external cause. The little Monad, parasitic on the eye-worm of the perch, which alternately spins round like a top, and then darts forward like an arrow, seems as if, like a watch, it required to be wound up before it could go.

Before I confine myself to those motive organs which are local, and planted in certain parts of the body of an animal, as legs, wings, fins, &c., I shall first mention those motions in which the whole body is concerned. Of this description, is the alternate contraction and expansion of some, as the Salpes and Pyrosomes and other Tunicaries; the annular motion propagated from one extremity of the body to the other, as in the earth-worms, geometric caterpillars, and many other larves; the undulating movements of the flexile bodies of many aquatic animals, as fishes, particularly the serpentiform ones; and the gliding motion of serpents themselves over the surface of the earth as well as their undulations. Many of the animals here alluded to are provided with subsidiary organs-as the earth-worm with lateral bristles; the geometric larves, with legs at each extremity of their body; the leech with suckerswhich, however, would be of little use without the expansion and contraction of its body; and the fishes with fins; but if

1 Phytozoa.

4 Diplostomum volvans.
6 See p. 120, 122.
9 Ibid. p. 181.

2 See above, p. 83.
5 See Appendix.
7 Ibid. p. 184.

3 Ibid, 82.

8 Ibid.

we consider the form and circumstances of all these animals, we shall see, in each case, the design and contrivance of Supreme Wisdom. Without the power of contraction and expansion, by which the Salpes, Pyrosomes, &c., alternately attract and repel the waters which they inhabit, they might indeed, from their absorbent structure, be saturated, but nutrition could not take place. The earth-worm again, a subterranean animal, but which occasionally emerges, by, the annular motion. of its body can much more easily wind its sinuous way without obstruction, when it seeks again its dark abode under the earth. The denser medium compared with air, through which the aquatic animals pass, renders great flexibility a very important quality, to enable them to overcome the resistance it opposes to their progress.

Having premised these observations on motions produced by the action of the whole body, or successively propagated from one extremity to the other, I shall now proceed to consider those external organs, which are its obvious instruments in the great majority of animals, beginning with those that are found in the lowest groups.

1. Rotatory Organs. In some species of Infusories, even in Ehrenberg's first Family of his Polygastric Class, the oral aperture is fringed with a circlet of bristles, but whether the animal by their means creates a vortex in the water, or whether they are analogous to the tentacles of the polypes, and are employed in collecting its food, seems not to have been clearly ascertained. Lower down in this Class, and approaching the Rotatories, we find a singular animal,' with bristles, by their position, simulating legs, which, as was before observed, revolve with wonderful rapidity. But it is in the Class of Rotatories that these revolving organs are most conspicuous. They are described as shaped like a tunnel, the tube of which terminates in a deep-seated pharynx, armed with jaws, and the external dilated orifice fringed with fine hairs or bristles, to which the animal communicates a very rapid rotation, whence they are called wheel-animals. Some, as the vorticels, the wheel-animals, by way of eminence, appear to have

1 Discocephalus Rotator, PLATE I. A. FIG. 6.

2 See Appendix.

3 Vorticella. Mall. They constitute chiefly the Rotifera of Lamarck, and are divided by Ehrenberg into numerous genera. His genus Vorticella, the type of which is V. convallaria, Mull., is placed in his Polygastric Class, in a section of his fourth Family, (Anopisthia,) which section he names Vorticellina.

two wheels, others thrce, or even four: Lamarck is of opinion, from the observations of Du Trochet, that what are taken for two or more wheels, are only one, bent so as to form partial ones;1 but in some they are certainly distinct organs. The object of the rapid gyration of this wheel, or wheels, is to create a vortex in the water, whose centre is the mouth of the animal, a little charybdis, bearing with it all the animalcules or molecules that come within its sphere of action, and by this remarkable mechanism it is enabled by its Creator, as long as it is encircled by a fluid medium, to get a due supply of food. These wheels are merely foraging organs, for, on a surface, the locomotions of these singular animals resemble those of the leech described in another place.3

In surveying the organs by which animals procure their food, we are struck by the wonderful diversity and multiplicity of means by which the same end is attained, and yet, through all this diversity, a series of approximations may be traced, proving that the same hand directed by the Wisdom, Power, and Love of one and the same Infinite Being, fabricated the whole host of creatures endowed with powers of voluntary motion. What care does it manifest, and attention to the welfare of these invisibles, and what contrivance, that they should be fitted with an organ, by means of which, when they are awakened from a state of suspended animation, and from a long fast, perhaps, of months, or even years, by water coming in sufficient contact with them, they can start up into life, and by the gyrations of their wheels immediately begin to breathe, and to procure a sufficient supply of food for their sustenance, while they continue animated.

2. Tentacles. Nearly related to these bristle-crowned rotatory appendages of the mouth of some animalcules are what are named Tentacles, so called probably from their being usually exploring organs. In its most restricted sense, this term is understood to signify organs, appendages of the mouth, which have no articulations, but, in a larger sense, the term has been applied also to all jointed organs in its vicinity, and used for a similar purpose, which, indeed, are the precursors of feelers and antennæ. The structure of the first-mentioned, or proper tentacles, and the means by which they perform their motions, and fulfil their functions, have been before explained. It is to these organs, as well as for their food, that the polypes are

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