poles with as good tails for swimming as any of their kindred, although as tadpoles they never enter the water; that the Guinea-pig is furnished with incisor teeth which it never uses, as it sheds them before birth; that embryos of mammals and birds have branchiul slits and arteries running in loops, in imitation or remi niscence of the arrangement which is permanent int fishes; and that thousands of animals and plants havo rudimentary organs which, at least in numerous cases, are wholly useless to their possessors, etc., etc. Upon a derivative theory this morphological conformity is explained by community of descent; and it has not been explained in any other way.

Naturalists are constantly speaking of "related species," of the "aflinity" of a genus or other group, and of "family resemblance "-vaguely conscious that these terms of kinship are something more than mero metaphors, but unaware of the grounds of their aptness. Mr. Darwin assures them that they have been talking derivative doctrine all their lives-as M. Jour dain talked prose-without knowing it.

If it is difficult and in many cases practically impossible to fix the limits of species, it is still more so to fix those of genera; and those of tribes and families are still less susceptible of exact natural circumscription. Intermediate forms occur, connecting one group with another in a manner sadly perplexing to systematists, except to those who have ceased to expect absolute limitations in Nature. All this blending could hardly fail to suggest a former material connec tion among allied forms, such as that which tho hypothesis of derivation demands.

Hore it would not be amiss to consider the general principle of gradation throughout organic Nature-a principle which answers in a general way to the Law of Continuity in the inorganic world, or rather is so analogous to it that both may fairly be expressed by the Leibnitzian axiom, Natura non agit saltatim. As an axiom or philosophical principle, used to test modal laws or hypotheses, this in strictness belongs only to physics. In the investigation of Nature at large, at least in the organic world, nobody would undertake to apply this principle as a test of the validity of any theory or supposed law. But naturalists of enlarged views will not fail to infer the principle from the phenomena they investigate-to perceive that the rule holds, under due qualifications and altered forms, throughout the realm of Nature; although we do not suppose that Nature in the organic world makes no distinct steps, but only short and serial steps-not infinitely fine gradations, but no long leaps, or few of them.

To glance at a few illustrations out of many that present themselves. It would be thought that the dis tinction between the two organic kingdoms was broad and absolute. Plants and animals belong to two very different categories, fulfill opposite offices, and, as to the mass of them, are so unlike that the difficulty of the ordinary observer would be to find points of comparison. Without entering into details, which would fill an article, we may safely say that the difficulty with the naturalist is all the other way-that all these broad differences vanish one by one as we approach the lower confines of the two kingdoms, and that no abso

lute distinction whatever is now known between them. It is quite possible that the same organism may bo both vegetable and animal, or may be first the one and then the other. If some organisms may be said to be at first vegetables and then animals, others, liko. the spores and other reproductive bodies of many of the lower Alge, may equally claim to have first a charac teristically animal, and then an unequivocally vegetable existence. Nor is the gradation restricted to theso simple organisms. It appears in general functions, as in that of reproduction, which is reducible to the same formula in both kingdoms, while it exhibits close approximations in the lower forms; also in a common or similar ground of sensibility in the lowest forms of both, a common faculty of effecting movements tending to a determinate end, traces of which pervade tho vegetable kingdom-while, on the other hand, this indefinable principle, this vegetablo

“Animula vagula, blandula,

Hospes comesque corporis,"

graduates into the higher sensitiveness of the lower class of animals. Nor need wo hesitate to recognizo the fino gradations from simple sensitiveness and volition to the higher instinctive and to the other psychical manifestations of the higher bruto animals. The gradation is undoubted, however we may explain it.

Again, propagation is of one mode in the higher animals, of two in all plants; but vegetative propaga. tion, by budding or offshoots, extends through tho lower grades of animals. In both kingdoms thoro

may bo separation of the offshoots, or indifference in this respect, or continued and organic union with the parent stock; and this either with essential independence of the offshoots, or with a subordination of these to a common whole; or finally with such subordination and amalgamation, along with specialization of function, that the same parts, which in other cases can be regarded only as progeny, in these become only members of an individual.

This leads to the question of individuality, a subject quite too large and too recondite for present discussion. The conclusion of the whole matter, however, is, that individuality—that very ground of being as distinguished from thing-is not attained in Nature at one leap. If anywhere truly exemplified in plants, it is only in the lowest and simplest, where the being is a structural unit, a single cell, memberless and organless, though organic-the same thing as those cells of which all the more complex plants are built up, and with which every plant and (structurally) every animal began its development. In the ascending gradation of the vegetable kingdom individuality is, so to say, striven after, but never attained; in the lower animals it is striven after with greater though incom plete success; it is realized only in animals of so high a rank that vegetative multiplication or offshoots are out of the question, where all parts are strictly members and nothing else, and all subordinated to a common nervous centre-is fully realized only in a conscious person.

So, also, the broad distinction between reproduc tion by seeds or ova and propagation by buds, though

perfect in some of the lowest forms of life, bocomos evanescent in others; and even the most absolute law we know in the physiology of genuine reproduction-that of sexual coöperation-has its exceptions in both kingdoms in parthenogenesis, to which in the vegotable kingdom a most curious and intimate series of gradations leads. In plants, likewise, a long and finoly graduated series of transitions leads from bisextat to unisexual blossoms; and so in various other respects. Everywhere we may perceive that Naturo secures her ends, and makes her distinctions on the whole manifest and real, but everywhere without abrupt breaks. We need not wonder, therefore, that gradations botween species and varieties should occur; the more so, since genera, tribes, and other groups into which the naturalist collocates species, are far from being always absolutely limited in Nature, though they are necessarily represented to be so in systems. From the nocessity of the case, the classifications of the naturalist abruptly define where Nature more or less blends. Our systems are nothing, if not definite. They express differences, and some of the coarser gradations. But this evinces not their perfection, but their im perfection. Even the best of them are to the system of Nature what consecutive patches of the seven colors are to the rainbow.

Now the principle of gradation throughout organic Nature may, of course, be interpreted upon other as sumptions than those of Darwin's hypothesis-certainly upon quite other than those of a materialistio philosophy, with which wo ourselves layo no sym• pathy. Still wo conceive it not only possible, but