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It will be seen that the method of restoration here contended for, is based on the alleged physiological necessity of the connexion between these several peculiarities. The argument used is, not that a scapula of a certain shape may be recognized as having belonged to a carnivorous mammal because we always find that carnivorous mammals do possess such scapulas; but the argument is that they must possess them, because carnivorous habits would be impossible without them. And in the above quotation Cuvier asserts that the necessary correlation which he considers so obvious in these cases, exists throughout the system: admitting, however, that in consequence of our limited knowledge of physiology we are unable in many cases to trace this necessary correlation, and are obliged to base our conclusions upon observed coexistences, of which we do not understand the reason, but which we find invariable.

Now Professor Huxley has recently shown that, in the first place, this empirical method, which Cuvier introduces as quite subordinate, and to be used only in aid of the rational method, is really the method which Cuvier habitually employed–the so-called rational method remaining practically a dead letter; and, in the second place, he has shown that Cuvier himself has in several places so far admitted the inapplicability of the rational method, as virtually to surrender it as a method. But more than this, Professor Huxley contends that the alleged necessary correlation is not true. Quite admitting the physiological dependence of parts on each other, he denies that it is a dependence of a kind which could not be otherwise. “Thus the teeth of a lion and the stomach of the animal are in such relation that the one is fitted to digest the food which the other can tear, they are physiologically correlated; but we have no reason for affirming this to be a necessary physiological correlation, in the sense that no other could equally fit its possessor for living on recent flesh. The number and form of the teeth might have been quite different from that which we know them to be, and the construction of the stomach might have been greatly altered; and yet the functions of these organs might have been equally well performed.”

Thus much is needful to give an idea of the controversy. It is not here our purpose to go more at length into the evidence cited on either side. We simply wish to show that the question may be settled deductively. Before going on to do this, however, let us briefly notice two collateral points.

In his defence of the Cuvierian doctrine, Professor Owen avails himself of the odium theologicum. He attributes to his opponents “the insinuation and masked advocacy of the doctrine subversive of a recognition of the Higher Mind.” Now, saying nothing about the questionable propriety of thus prejudging an issue in science, we think this is an unfortunate accusation. What is there in the hypothesis of necessary, as distinguished from actual, correlation of parts, which is particularly in harmony with Theism? Maintenance of the necessity, whether of sequences or of coexistences, is commonly thought rather a derogation from divine power than otherwise. Cuvier says–“None of these parts can be changed without affecting the others; and consequently, each taken separately, indicates and gives all the rest.” That is to say, in the nature of things the correlation could not have been otherwise. On the other hand, Professor Huxley says we have no warrant for asserting that the correlation could not have been otherwise; but have not a little reason for thinking that the same physiological ends might have been differently achieved. The one doctrine limits the possibilities of creation; the other denies the implied limit. Which, then, is most open to the charge of covert Atheism?

On the other point we lean to the opinion of Professor Owen. We agree with him in thinking that where a rational correlation (in the highest sense of the term) can be made out, it affords a better basis for deduction than an empirical correlation ascertained only by accumulated observations. Premising that by rational correlation is not meant one in which we can trace, or think we can trace, a design, but one of which the negation is inconceivable (and this is the species of correlation which Cuvier’s principle implies); then we hold that our knowledge of the correlation is of a more certain kind than where it is simply inductive. We think that Professor Huxley, in his anxiety to avoid the error of making Thought the measure of Things, does not sufficiently bear in mind the fact, that as our notion of necessity is determined by some absolute uniformity pervading all orders of our experiences, it follows that an organic correlation which cannot be conceived otherwise, is guaranteed by a much wider induction than one ascertained only by the observation of organisms. But the truth is, that there are relatively few organic correlations of which the negation is inconceivable. If we find the skull, vertebrae, ribs, and phalanges of some quadruped as large as an elephant; we may indeed be certain that the legs of this quadruped were of considerable size–much larger than those of a rat; and our reason for conceiving this correlation as necessary, is, that it is based, not only upon our experiences of moving organisms, but upon all our mechanical experiences relative to masses and their supports. But even were there many physiological correlations really of this order, which there are not, there would be danger in pursuing this line of reasoning, in consequence of the liability to include within the class of truly necessary correlations, those which are not such. For instance, there would seem to be a necessary correlation between the eye and the surface of the body: light being needful for vision, it might be supposed that every eye must be external. Nevertheless it is a fact that there are creatures, as the Cirrhipedia, having eyes (not very efficient ones, it may be) deeply imbedded within the body. Again, a necessary correlation might be assumed between the dimensions of the mammalian uterus and those of the pelvis. It would appear impossible that in any species there should exist a well-developed uterus containing a full-sized foetus, and yet that the arch of the pelvis should be too small to allow the foetus to pass. And were the only mammal having a very small pelvic arch, a fossil one, it would have been inferred, on the Cuvierian method, that the foetus must have been born in a rudimentary state; and that the uterus must have been proportionally small. But there happens to be an extant mammal having an undeveloped pelvis–the mole–which presents us with a fact that saves us from this erroneous inference. The young of the mole are not born through the pelvic arch at all; but in front of it! Thus, granting that some quite direct physiological correlations may be necessary, we see that there is great risk of including among them some which are not.