ence by a life of ceaseless activity and toil, others are formed for parasitic attachment to the living tissues of larger animals, and there find life and enjoyment without a single effort or care of their own. And as these varied functions necessarily require for their performance a special adaptation of organs—a tooth to cut or a tooth to grind, a foot to seize or a foot to dig, a limb to run or a limb to fly—so will similar modifications afford to the palaeontologist an evidence of functions performed in bygone ages, and enable him, not only to reconstruct forms of harmonious, organs, but to assign to these organs the part they had to play in the great drama of vitality. In the performance of these varied functions many animals have to make long periodic migrations, either for the immediate purpose of procuring food and shelter for themselves, or prospectively for their future young. From colder to warmer regions, and from warmer to colder-from land to water, and from water to land-from sea to river, and from river to sea-there is ever, among certain animals, an incessant interchange; and though palæontology has yet been unable to detect such migrations in the past, we may rely on their occurrence, and be prepared to admit the fact into our inferences and reasonings.

Coexistent with and beyond all this, there are those innumerable differences of species and kind and family and class, which we can only resolve into the eternal will of the Creator. Why, for instance, should the polype differ from the star-fish, the star-fish from the crab, the crab from the turtle, the turtle from the fish, the fish from the bird, or the bird from the quadruped? It is in vain to tell us that the one is but a progressive or developmental form of the other—that the reptile is but a transmutation, in time and under new external conditions, from the fish, and that the fish is but the lineal descendant of the shell-fish. Admit

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ting that such was the true genetic origin of the various grades of vitality, there still lies behind and unaccounted for the orderly plan in which such development shall occur, and the reason for the definite specific forms which the descendants invariably assume. Grant, we again repeat, that all vitality were indissolubly interwoven into one great genetic mesh, still that mesh presents, at determinate times and over determinate areas, definite variety and speciality of pattern. Whence this orderly variety? Wherefore these special and distinctive patterns? At the most, Science can only note the distinctions, it can never hope to assign the reason. To do so would be to place the intelligence of the finite creature on the same level with the prescience of the infinite Creator. It is our high privilege, however, to observe and reason; and, reasoning, to arrange and classify the animal kingdom according to their different grades and affinities, and so arrive at some intelligible comprehension of the great scheme of vitality.

As in Botany, so in Zoology this arrangement is greatly facilitated by the fact that, numerous as animal forms are, they are all constructed after a few primal types and patterns. Some are furnished with a bony skeleton, the leading feature of which is the vertebral column or backbone— these are the VERTEBRATES; others have no such osseous framework-these constitute the INVERTEBRATES. As the leaf was the primary organ in the plant's development, so the vertebra seems to be the primal organ in the vertebrate skeleton; and by its modifications and adaptations for special ends, the Creator has produced every form of terrestrial, aërial, and aquatic existence. According to the modern. doctrines of anatomy, the skull, or brain-case, is composed of vertebral bones, modified and adapted for a special purpose so are the limbs, whether for running, flying, or swimming; so also the ribs, whatever their form or num

ber; and in like manner all the other appurtenances of the vertebrate skeleton. This is the great doctrine of HOмOLOGY, or science of similar parts, as it is termed, through which we arrive at the conclusion that the arm and hand of man, the fore-limb and foot of the quadruped, the wing of the bird, and the fore-fin of the fish, are one and the same primal organ, composed of the same or homologous parts, and merely modified or altered for the performance of certain special functions. As the stationary engine that turns the spindles of the factory, the locomotive that drags the railway cars, and the marine engine that propels the steamship, are but modifications of the same primal machine; so the mammal that runs, the mammal that flies, and the mammal that swims, are but specialised expressions of the same primal plan, the creation of a new type being unnecessary where a modification of an existing one would suffice. Knowing these modifications in the limbs, jaws, teeth, and other organs, and the ends they were meant to subserve in living races, we can predicate of forms long since extinct, and can associate with co-relation of structure the functions that creatures were meant to perform in the economy of former ages. It is by this "law of the co-relation of parts," and faith in the uniformity of nature's method, that Cuvier and Owen, and other great anatomists, have been enabled to accomplish their wonderful restorations of extinct life, and from a few sorely mutilated and scattered fragments to present us with forms of harmonious entirety. "Every organised being," says the great French anatomist, "forms a whole, a single circumscribed system, the parts of which mutually correspond and concur to the same definite action by a reciprocal reaction. None of these parts can change without the others also changing, and consequently each part, taken separately, indicates and gives all the others." As with the vertebrate type, so with the molluscan, the

articulate, and the radiate. There is a plan and primal pattern to each, and that plan, modified and specialised, can be traced through every species and individual of the division, no matter how varied and numerous they may be. And what has been done to homologise the external framework will shortly be done for the muscular, respiratory, and vascular systems-for the organs of digestion, secretion, and reproduction-so that we may no longer combine things that are merely analogous with those that are homologous, and thus confound, in our interpretations of nature, beings that were from the first constructed on an essentially different basis.

Proceeding on grounds such as these, the zoologist separates the vertebrate from the invertebrate, the mammals from the birds, the birds from the reptiles, and the reptiles from the fishes. He also separates the invertebrate shell-fish from the invertebrate crab, the crabs from the sea-urchins, the sea-urchins from the star-fishes, the starfishes from the corals, and these again from the lower sponges that can scarcely be distinguished from the seaweeds that surround them. Looking at the manner in which the functions of nutrition, reproduction, and sensation are performed in each of these classes, we speak of "higher" and "lower" forms, of creatures of more simple and of more complex organisation; but we do not say—and reason and experience alike shrink from endorsing the allegation that one form or family is less perfect than another, either in its nature or in the functions it was designed to perform.

"All are but parts of one stupendous whole,
Whose body Nature is, and God the soul;
That changed in all, and yet in all the same;
Great in the earth as in the ethereal frame;
Warms in the sun, refreshes in the breeze,
Glows in the stars, and blossoms in the trees;

Lives through all life, extends through all extent,
Spreads undivided, operates unspent;

Breathes in our soul, informs our mortal part,

As full, as perfect in a hair as heart;

As full, as perfect in vile man that mourns,
As the rapt seraph that adores and burns;
To him no high, no low, no great, no small,

He fills, he bounds, connects, and equals all."

While thus disclaiming the idea of "imperfection" as applicable to any grade of vitality, it would be erring against all reason and instinct to discard the terms " 'higher" and "lower" in treating of organised existences. The creature consisting of a uniform mass must appear, even to the most untutored observer, to stand on a humbler platform than that composed of a variety of parts and tissues. The protozoan, that envelops its food in its gelatinous sac, assimilates the nutritive juices, and then rejects the remainder, and this without mouth, stomach, or opening of any kind, is certainly lower (or less highly organised, if you will) than the mollusc, which is furnished with mouth, stomach, and alimentary canal; and the mollusc, furnished only with external gill-tufts and the merest heart-like cavity, can never be placed on the same level with the quadruped provided with masticating and salivatory apparatus, its stomach, its organs of chylification and chymification and intestinal canal-its respiratory and circulating system of lungs, heart, veins, and arteries. Again, the protozoan that reproduces itself by a mere cellular expansion of its own mass-a mass, any portion of which is equally vital, and capable of becoming a separate creatureis surely lower in the scale than the shell-fish that reproduces by spawn, and would perish under subdivision of its tissues; while the reptile, reproducing by eggs, which it drops in the stagnant pool and never cherishes, can never, without the abuse of everything like discrimination, be