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them, connecting types with embryonic characters. This is not an isolated fact, but one which meets us at every step in the course of our study of the geologic history of the earth. It is but one illustration of a general law, a law of the deepest philosophic import, and yet one which is still very imperfectly recognized among geologists. The law may be thus stated: The first introduced animals or plants of any class have been combining types, i. e., have united within themselves the characters of several families, now distinct and even widely sepa rated. Thus the first vertebrates introduced were fishes, but not typical fishes, as we might be led a priori to expect, but Placoids and Ganoids, families which, particularly in their earlier representatives, united with ordinary fish characters others which connected them with the class of reptiles, and even of mammals; and still others which connect them with the embryonic condition of the typical fishes. It is this combination of embryonic characters with others which connect them with the higher classes, this union of high and low characters, which has given rise to all the dispute concerning the position of these families in the scale of Fishes as well as to much of the difference of opinion concerning the law of succession of animals in Geology. Again, the first introduced reptiles, viz: the reptiles found in the old red sandstone and coal, are the most remarkable instances of connecting types of which we have any knowledge. In the first place they seem to have been amphibious, (in the proper sense of the word,) and thus to have connected land animals and water animals, air breathing with water breathing, and all of them united characters, which are now represented by widely separated families. To give a single instance: the carboniferous reptile, recently described by Professor Wyman and exhibited at the last meeting of the Scientific Association at Albany, so remarkably combined characters which are now parcelled out between the three families of Batrachians, Saurians, and Ophidians, that this distinguished comparative anatomist seemed almost at a loss as to which of these families to assign it. He decided, however, that it most nearly resembled a Salamandroid Batrachian with characters closely connecting it with the other families already mentioned.

The Labyrinthodon of the new red sandstone has been classed by some anatomists with Batrachians, and by others with crocodiles. There seems yet a doubt whether it should be called a tailless crccodile or a crawling frog with crocodilian teeth. The huge Saurians of the secondary period combined reptilian with fish, and even some mammalian characters. Even in the tertiary period and in the introduction of the highest animals this law is not forgotten. The recent investigations of Professor Owen have shown that the first introduced Pachyderms were not typical Pachyderms, but that they combined the characters of Pachyderms and Ruminants to such a degree that it is almost impossible to assign them with certainty to one or the other order. In fact, the study of these extinct forms has led this great anatomist to class the Pachyderms and Ruminants together as subdivisions of one and the same order.

Thus in every case in the earliest fauna and floræ one class stood for many. The earliest families combined the characters of several

families or classes, and stood as their representative until these famialies or classes were separately introduced. The Placoids and Ganoids, for instance, stood during almost the whole paleozoic period the sole representatives of the vertebrate type, combining in themselves the characters of all classes, and thus prophesying their coming, until Nature was fully prepared for their introduction. The Sigillaria and Lepidodendron stood as the representatives of both Cryptogam and Phonogam, until these two ideas were separately and more distinctly expressed by the subsequent introduction of the typical forms of these two classes. It is as if Nature first sketched out her work in general terms and then elaborated each subordinate idea in separate families; all these families, taken together as an organic whole, still containing the original idea in a more completely developed form, as if the problem of organic nature was first expressed in a few simple but comprehensive symbols and then differentiated. Organic nature has often been compared to a broken chain, the disjointed links of which are the widely separated and distinctly marked families of the present fauna and flora, and the connecting links of which are to be found deep buried in the strata of the earth. But the complexity, the beauty, and, more than all, the life, growth, and development of Nature, is not to be represented by any such miserable mechanical contrivance as a chain. It is rather a tree-a tree of life-a tree whose trunk is deeply rooted in the lowest palæozoic strata, whose first giant arms are given off in the carboniferous, which branch again in the secondary and again in the tertiary periods, while its extreme branchlets, and also its flower and fruit, are the fauna and flora of the present epoch. The object of geology is to trace each branch to its fellow branch, and each limb to its fellow limb, and thus gradually to restore the whole noble form and determine the laws of its growth.

This differentiation, this passing from simplicity to complexity, from unity through diversity to a higher unity, is the fundamental law of development. Let me illustrate my meaning by a few simple examples: The ultimate anatomical elements of every organized body, whether animal or vegetable, are cells. The whole body is made up of cells, and all the bodily functions are performed by cells. In fact, the body may be looked upon as an organized community of individual cells. Now, if we trace these cells from their earliest condition in the embryo to their mature condition in the fully developed animal or plant, or from the lowest animal or plant regularly to the top of the scale, we will observe a most beautiful instance of the differentiation of which I speak. The cells are at first all alike, simple and globular, and each performs all the functions appertaining to cells, though comparatively imperfectly. But as development advances the cells begin to take on different forms and to perform different functions. Some become nervous cells, some muscular cells, some biliary cells, &c., until, in the mature condition and in the highest animals, the diversity of form and specialization of function reaches the highest point, each form of cell being confined to the performance of a single function.

If, instead of the ultimate anatomical elements, the cells, we take the proximate anatomical elements, the organs, or even the regions of

the body, still the same differentiation of form and specialization of fuction is observable as we pass from the embryonic to the mature condition, or from the lowest to the highest animals. I might give many other examples taken from the organic kingdom. I will give but one other example, and that taken from a still higher kingdom. Human society is also an organized body, the ultimate anatomical elements of which are individuals. Now, in the earliest conditions of human society we find these elements, so far as their social functions are concerned, identical. Each man performs all the social functions apertaining to man. He is his own tailor, shoemaker, agriculturist, scientific man, &c. But in proportion as society advances in the same proportion does specialization of social functions advance, until, if we could conceive of a society perfectly organized on a purely material basis, i. e. according to the French material philosophy, then the social function of each individual would be reduced to the narrowest possible limits. This is only impossible or undesirable on account of man's moral and spiritual nature. Still it is no less evident that, in so far as human society is a material organization, specialization of function, differentiation is the law of development.

Now, it will be recollected that in the geological history of animals and plants we have everywhere found the same differentiation of form and specialization of function. As in the history of the animal body, one cell form in the embryo was the representative of many widely separated cell forms in the mature animal; so also in the geological history of that greater and more complex organism, the animal and vegetable kingdom, one form in the early periods stood as the representative of many widely separated forms in its present mature condition. Am I not justified, then, in saying that the great law which has governed the introduction of successive animal and vegetable species is that of gradual development of the animal and vegetable kingdom as an organic whole?

It seems to me that all the dispute and misunderstanding on this subject have been the result of too narrow a view, have arisen from fixing the mind upon genera and species instead of upon the larger divisions of classes and orders, upon the individual elements instead of the organic whole. Development does not necessarily involve the idea of progression in all the individual elements. In the differentiation of the cells of the living body, of the individuals of an advancing community, or of the forms of an advancing fauna, the whole organism progresses, but as a necessary result of differentiation, while the highest individuals are successively higher and higher, the lowest, considered in themselves, and not as parts of an organized whole, may become lower. Certainly the difference between the high and the low becomes constantly greater. It should not surprise us, then, that some of the lowest forms of animal life have been among the latest introduced. It is precisely what, according to a true appreciation of the law of development, we should be naturally led to expect.

Mr. Hugh Miller, the eminent Scotch geologist, in his admirable work, "Footprints of the Creator," by taking too limited a view of this subject, has been led, if not into error, at least into a statement of views which has misled many. In his zeal against the Lamarck

ian theorists, and more particularly against the author of the "Vestiges of Creation," he has attempted to show that, in certain families, at least, the law has been that of degradation, instead of progression. He has labored to prove that the earliest fishes have been the highest, instead of the lowest fishes, and that the earliest reptiles have been higher in the scale than the present reptiles. This idea has been seized upon by some in this country, and it has been attempted, by connecting it with the fall and degradation of man, to show that the universal law of history, both geological and human, is degradation. The disciples of this melancholy philosophy believe that divine power successively introduced higher and higher classes, but each class, left to its own laws, continued to degrade itself. The Deity repeatedly attempted progression, by the miraculous introduction of successively higher classes, but some malign influence as constantly interposed and, to some extent, frustrated these attempts.

Now, it is evident that these theorizers have never thoroughly grasped the fundamental idea of development. They mistake specialization for degradation. Upon this theory all our boasted modern civilization, so far as it is the result of division of labor, specialization of social functions, and mutual dependence of parts, is degradation.

Upon what ground are the Ganoids and Placoids considered the highest fishes? Only on the ground that they combine with their fish characters others which ally them with the higher classes, particularly with reptiles. In other words, they fall into the very error of the Lamarckians themselves, viz: that of supposing that the animal kingdom is to be represented by a linear series, and that, therefore, the highest fishes approach the lowest reptiles, and the highest reptiles the next higher class, &c. But the very reverse of this is the fact. The animal kingdom should be represented by an infinitely branching tree, rather than by an ascending right line; for we find, in every case, classes approach each other in the lowest members of each, and diverge as they ascend. Thus, it is the lowest, and not the highest plants, which approach the animal kingdom. As we ascend, they become more and more widely separated, until, in the highest representatives of each, the separation reaches its highest point. So also each branch of these kingdoms diverges from its fellow branches. It is, therefore, in its lowest, not its highest, members that we should naturally expect, according to the law of differentiation, the class of fishes to approach the class of reptiles. In some sense, indeed, Placoids and Ganoids may be considered higher than typical fishes. Their brain and nervous system is more highly organized, their reproduction is more complex, their young are better cared for. But it will be recollected that they are both connecting and embryonic types. Now, it is their connecting characters which seem to elevate them, for their true fish characters are all embryonic. As vertebrates they may possibly be considered higher than other fishes, but as fishes they must be considered low. Anatomists may place them high but morphologists will always place them low. If the several classes of the animal kingdom, diverging in various directions, be, as it were, projected upon a vertical plane, the Placoids and Ganoids may possibly occupy a higher position than the typical fishes; but,

in such a rectilinear projection, all the variety and beauty of nature is lost. It is evident that, for purposes of classification, the morphologist is right; for if the principle of the anatomists is consistently carried out, no classification is possible, for animals the most diverse, an echinoderm and a fish, may be brought together. The Divine classifier, in the introduction of species, has followed the principle of the morphologist.

Geology, then, teaches, and, as it seems to me, unmistakably teaches, that the law of succession of animals and plants is that of progressive development in time of these two kingdoms. But, although there has been a development, it is not the development of the Lamarckian, of the author of the Vestiges of Creation, and the pantheist. The development which geology teaches is not a development which is the result of physical laws and physical forces. If there is anything which geology teaches with clearness, it is that the animal and vegetable kingdoms did not commence as monads, or vital points, but as organisms so perfect that even the maddest Lamarckian must admit that they could not have been formed by agency of physical forces; that species did not pass into one another by transmutation, but that each species was introduced in full perfection, remained unchanged during the term of their existence, and died in full perfection; that physical conditions cannot change one species into another, but that a species will give up its life rather than its specific character. In passing from the equator to the poles we pass from one geographical fauna to another, from one set of species to another, but observe no transmutation, but only substitutions; so also in passing from the oldest geological to the present fauna we pass from one set of species to another; not, however, by transmutation, but always by substitution. This has been repeated so many thousand times in the geological history of the earth that there is no room for doubt on the subject. As far as the evidence of geology extends, each species was introduced by the direct miraculous interference of a personal intelligence. There has, indeed, been a constantly increasing series, but the connexion between the terms of the series has not been physical or genetic, but intellectual; not founded in the laws of reproduction, but in the eternal counsels of the Almighty. There has, indeed, been a development, but not a development the force of which exists within the thing developing; but rather the development of a great work of art, under the hand of the Divine Artist-a work conceived in eternity, and elaborated throughout all time. What an overwhelming idea this thought gives us of the unchangeableness, the all-comprehensive intelligence and foreknowledge of the Deity! The infinite diversity of nature, the whole idea of this infinite work of art, was contained in the first strokes of the Great Artist's pencil, and the ceaseless activity of Deity has been exercised only in the eternal unfolding of the original conception.

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