planetary bodies in particular, and it is an instructive circumstance, that in consequence of the advance of knowledge, we are able to unfold a greater number than could be developed in the days of Paley. There is no just ground, then, for the scoffing remark of the haughty and eccentric Frenchman, (who denies that he is an atheist, seeing that he adores himself and has set up a formal worship of his system,) that the heavens cannot now be appealed to as a proof of the existence of Deity, or for the inference drawn by him, that the time will speedily arrive when organized objects will be in the same condition; for while, for the reasons stated, animals and plants must ever furnish the most striking examples of design, it is still true that "

THE HEAVENS DECLARE

THE GLORY OF GOD, AND THE FIRMAMENT SHOWETH HIS HANDIWORK."

BOOK THIRD.

THE INTERPRETATION OF THE FACTS.

CHAPTER I.

THE ARGUMENT FROM COMBINED ORDER AND ADAPTATION.

WE are now to estimate the force of the influence of two streams, which we have hitherto been contemplating as flowing in parallel channels.

The principle of Order has been scientifically expounded only in modern times, and in regard to the animal and vegetable kingdoms only within these few years. But it existed from the creation of the world, and had been noticed in a general way since the creation of intelligent being. Science in its latest advances is simply coming up to, and explaining, the spontaneous suggestions of human thought, which as it muses upon the universe is at once struck with the model forms and correspondences which everywhere prevail. The late discoveries in regard to homotypes, homologies, and we may add homoeophytes, or parallel developments in animal and vegetable structures, is but the scientific exposition of what all along impressed intelligent observers, without their being able to give an account of it. Nor

are these remarkable facts of an isolated or exceptionable character; on the contrary, they are merely striking examples of what is universal, and they have their homotypes, analogues, homologues, and parallels, in every department of nature.

The principle of Special Adaptation, or that of particular conformity to the position of the object and function of the organ, has also been noticed all along by minds addicted to reflection. Socrates is represented by Xenophon as delighting to dwell upon it. So strong, indeed, was this tendency in the ancient world, and in the middle ages, that Bacon felt himself called on to remove the inquiry from physical science, where it hindered the discovery of physical agents, to metaphysics, where it might have a legitimate scope. Bacon was right in saying, that the propensity to discover final cause had sometimes come in the way of the discovery of physical cause; but he is altogether wrong in affirming that it is barren of results in scientific inquiry, for in certain departments of natural science, such as physiology and comparative anatomy, it is a most powerful instrument of discovery, and such eminent men as Cuvier and Sir Charles Bell delight to inform us that they have proceeded on the principle of final cause in all their researches.

It is not difficult to discover the beauty and the appropriateness of both these principles.

On the one hand, the mind discerns the need and appreciates the propriety of the principle of Order. Without some such governing principle, nature would be incomprehensible by human intelligence, and this because of the very number and multiplicity of the objects of which it presents, each eager to catch our notice; and the mind in trying to apprehend them would have felt itself lost, as in a forest through which there is no pathway, or as

in a vast storehouse, where the seeds of every species of plant on the earth's surface, are mixed in hopeless confusion. By what means is it that man is enabled to arrange into groups the objects by which he is surrounded, and thus acquire a scientific knowledge of them, and turn them to practical purposes? Plainly, by reason of the circumstance that there are numberless points of resemblance and correspondence between them. Scientific men have so long been familiar with this process that they are not impressed by it as they ought, and seldom do they inquire into the ground on which it proceeds. It is only when something new, such as the discovery of homologies in the animal kingdom, comes to light, that they are led to reflect on what has been too common to be specially noticed. But if they but seriously reflect on the subject, they will find that it is because of the universal prevalence of points of resemblance and correspondence that man is enabled to grasp the infinity of objects which fall under his view, into classes and subclasses, which can be comprehended by the intellect, and treasured up in the memory.

No doubt the mind has in itself a power of forming classes altogether independent of any special arrangement in order to aid it; but such groupings, though they may at times help the memory, are of no intellectual or scientific value. But there are means in nature of guiding the mind to the formation of classes which have a deep and far-reaching significance. It is true, in an important sense, that classes are already formed for us in nature. Man will find it expedient, in all cases, to attend to these arrangements made to his hand, and he must attend to them, provided he represent his classification as a natural one. It may illustrate our general subject to show what are the distinctive marks

of natural classes, that is, of classes having the sanction of nature.

And first, we may take a classification which is not of this description. It is conceivable that a person might arrange all animated beings according to their size. He might put all animals of a certain height in one class, and all animals below that in another class. Every one sees how arbitrary, in short, how contrary to nature, such a distribution would be. It would often separate animals belonging to the very same species, while it would put in one confused group bird and fish, mammal and insect. And why, it may be asked, does the naturalist at once reject such a classification? Perhaps it is answered, because he is seeking a natural arrangement. But this answer, though correct so far as it goes, does not go down to the depths of the subject, for we immediately ask, Is not the distinction of size a natural one? He who would really sound the depths of this subject, and not skim over it, must be prepared to state what is the difference between an artificial and a natural classification.

All natural classes will be found to have not merely one, but an aggregate of common attributes. It follows that, when objects are classified according to a natural arrangement, the possession of any one characteristic is a mark of a great many others. Thus, when an animal is described as a reptile, we know that its blood is cold, that its heart consists of three cavities, and that its young are produced from eggs; and when we hear an animal called by the name of mammal, we know not only that it suckles its young, but that it breathes by lungs, that its blood is warm, and that its heart consists of four compartments. In short, when we have fixed on a truly natural arrangement, the presence of any one characteristic becomes a sign of others, commonly of very many