Though Darwin's own belief, and the application which he makes of his theory, go much further than the assumed divergence of individuals into varieties, and of varieties into species, he wisely limits his main argument to the question of the origin of species; as this covers the whole ground of controversy between opposing parties. For if diverging varieties have never yet been able to break over the border line, which circumscribes species, they are not likely to achieve the feat of making the wider deviations into genera, families, orders, etc. But if, on the other hand, the descendants of a common stock may cross the nearest natural boundary, there is no good reason why they may not reach and successively pass over the remoter limits which have been supposed to divide organic beings.

As regards the nature and extent of the evidence on this question, Huxley remarks, "I do not know, that it is possible by direct evidence to prove the origin of a variety in nature, or to prove selective breeding." But as varieties within the limits of species are known to exist in the wild state, it is perfectly legitimate to ascribe their origin to the joint agency of the tendency to variation, observed in domestic species, and of any causes operative in nature, which may act a part analogous to that of selective breeding. Now it may be freely granted that Darwin, under the designation of natural selection, has called attention to the agency of causes of great potency, which obviously act in the manner and direction, which he ascribes to them. The only question is, are they adequate to perform the stupendous task, which he has set for them? He has satisfactorily accounted for the origin of varieties in the natural state by analogies drawn from domestic species, and by a most skillful and logical presentation of facts and arguments fully bearing out his conclusions. But is he entitled to go further and to claim, that species have originated like varieties through the agency of variability and natural selection? I think that impartial scientific criticism must decide that he has failed to establish the justice of such a claim.

It is but fair to admit, on the other hand, that a more indul

gent criticism finds much in Darwin's book to charm the imagination and win the reason to the acceptance of the theory set forth. There is something fascinating in the thought of a unity in multiplicity, bound into oneness by the all-pervading ties of genealogical descent and unlimited correlation of kindred forms. This thought has a peculiar attraction for those persons, who are mentally averse to that conception of unity which rests in the originating and controlling power and providence of an omnipotent Creator. Moreover, the style and manner of the author is such as naturally to conciliate the favor of the reader. There is an evidently honest aim at candor, quite remarkable in an earnest and enthusiastic advocate of a theory. Then this very enthusiasm is adapted to catch the sympathy of the reader and to drift him unconsciously into the views of the author.

Of course the reader has seen, in what has gone before, that there is more in this book than the glamour of magnificent generalizations, the fascination of a pleasing style, and the charm of a pervading enthusiasm. Laying aside all these, we have still left a broad basis of solid facts, supporting a superstructure of plausible speculation and argument.

Darwin's theory of the origin of species derives its show of validity from the fact that it assumes no new or unknown law of nature, but is a simple attempt to generalize and to extend the application of actual known laws of organization -laws which cover a wide range of the most interesting facts of biology. The law of development, which lies at the basis of the hypothesis, is no fiction of superficial scientists. Within a certain range it exercises a supreme and rightful sway over the facts which relate to the origin and growth of organized beings.

From the first appearance of the individual plant or animal till the stage of maturity is reached, much of the progress of change which takes place falls under the law of evolution or development. In the case of the frog we have the same individual passing from the form of a limbless animal, with welldeveloped tail, to that of a tailless quadruped, and from the

condition of fish-life to that of an air-breathing animal. In many insects we have three well-marked stages of development, under the forms of larva, chrysalis, and perfect insect. In the facts of embryology we have another exemplification of the great law of organic development. Von Baer has shown that the embryo of a higher form of organization passes in its progress of development through all the grades of the lower forms; so that if, in the class of vertebrates, the embryo becomes capable of individual life at an early stage of development, it will come forth a fish; if it becomes self-supporting at the next higher stage of evolution, it takes its place in the rank of reptiles; in the next higher grade we have the bird; in the highest of all, the mammal. Geologists recognize a remarkable parallelism between the successive stages of embryonic development and the succession of organized beings on the earth, as indicated by fossil remains.

It is not strange that such facts and analogies should have suggested to naturalists the guess, that species, genera, orders, classes, etc., may have originated from some common stock, through the operation of the laws of development, which are known to have so wide an application to the phenomena of the organic world. Whether this guess is to stand as a simple hypothesis, or is to take rank as a confirmed theory, correctly representing the order of nature in that department of phenomena to which it relates, is the question at issue.

It is an argument much relied upon by the partisans of the theory in question, that it renders intelligible the great system of nature, while, as they allege, the doctrine of especial creative interpositions is glaringly inconsistent with the sublime order everywhere observed. Many facts brought to light by comparative anatomy are claimed to be intelligible on Darwin's theory, but are declared to be utterly without significance on the theory of creative design. Compare the bones of the limbs of animals, and you will find a remarkable similarity, in number, form and connection, running through the great majority of the species which have existed in the past or still exist in the present. In one species every bone, however

minute, constitutes an essential part of a perfect and highly useful organ. In other species many of the bones are seemingly useless, and at best but rude imitations of their analogues in the more perfect species. These facts are assumed to be intelligible on the theory of the transformation of species, the imperfect bones being supposed to be either rudimentary forms left unfinished by arrested development, or the degenerated parts of organs which have fallen into decay by disuse.

This argument assumes that phenomena become intelligible by being referred to a general class, for which they have a real or imaginary resemblance, whether they can be proved essentially to belong to that class or not. Moreover, the allegation, that such facts are intelligible on Darwin's theory, but inconsistent with the doctrine of a designing Creator, is based on the assumption that the Creator, if there be one, ought always to confine himself to serious work, and not indulge in the diversion of playing with analogies by sketching in many species a plan which he brings to perfection in only a few. Whatever man may be allowed to do for innocent amusement or for the gratification of an artistic sense, it is assumed to be unbecoming the dignity of a Creator to depart in the slightest degree from the most rigid rule of utility.

We shall best estimate the weight of the arguments adduced in support of Darwin's theory by applying to them the test of the inductive logic. The highest authorities on the philosophy of the inductive sciences specify three steps in the procedure by which a theory may be constructed and established as the true representation of the facts and laws of nature, as regards the phenomena to which it is applied. The three steps of procedure in question are induction, deduction and verification. By induction we first infer a law from the observation of a limited range of related facts, and then hypothetically extend the application of that law over all other seemingly allied facts. This extension provisionally raises the supposed law to the rank of a general theory. By deduction we proceed to offer explanations, based on the supposed law, of all related known facts-assume that observation will confirm the applica

bility of the law to this wider range of phenomena to which it has been extended, and go on to predict, on the hypothetical validity of the law, other yet undiscovered facts. By verification we resort to experiment, observation and comparison, as the means of testing the validity of our deductions. If the tests confirm the deductions, so far, the theory is confirmed. If the tests fail, it is proof that there is some defect in the conception of the law, or that our induction has extended it beyond its legitimate range.

From a great multitude of organic phenomena, a law of evolution or development has been inferred, and, within certain limits, may be regarded as established. The theory of Darwin, by a bold induction, extends the application of this law to the supposed origination of all organic forms from a few primitive, simple forms, and assumes to set forth the conditions, physical and organic, through which such stupendous results have been accomplished.

Assuming the validity of this induction as a true representation of the facts of organization, the following are legitimate deductions from it:

1. By skillfully taking advantage of the tendency to variation and law of inheritance by selective breeding, we shall be able to bring about the transformations which the theory assumes to be constantly going on.

2. The theory will satisfactorily account for all organic phenomena at present known or yet to be discovered, as regards form, anatomical structure, instinct, habits, etc.

3. A closer observation of organic forms will show them imperceptibly graduating one into the other, without any distinct lines of demarcation between them; and this ought to be apparent, whether we direct our attention to the living races or to the remains of extinct forms.

4. The order of succession shown by organic remains ought to be from the simpler to the more complex, from the lower to the higher organic forms.

5. The geographical distribution of organic beings should conform to the genealogical relations, which the theory