within the scope of a very limited experience, it might safely be inferred that something much greater would be detected, if our range of experience were extended, especially since the world presents us with results which can only be naturally accounted for in this manner.'

As regards, however, the mode in which species have originated, the writer of the 'Vestiges' rejects the views of Lamarck altogether, considering his theory as to the cause of varieties (and therefore of species) as 'so far from adequate to account for the facts, that it has had scarcely a single adherent.' In this, the writer of the 'Vestiges' does less than justice to Lamarck. The special theory of the French naturalist does not fail because it gives the adaptive theory too much to do.' It fails because it does not recognise how useful adaptations are preserved and strengthened. It was left to the genius of Charles Darwin to fill this all-important hiatus in the Lamarckian hypothesis.

The author entirely accepts the conception of a fundamental unity of organisation among animals; and regards this as implying 'that all were constructed upon one plan, though in a series of improvements and variations, giving rise to the special forms, and bearing reference to the conditions in which each animal lives.' He points out that this underlying unity of organisation is of itself a strong à priori argument against the idea of the separate creation of species. Organisms,' he remarks, we know to have been produced, not at once, but in the course of a vast series of ages; here we now see that they are not a group of individually entire things accidentally associated, but parts of great masses, nicely connected, and integral in their

respective totalities. Time, and a succession of forms in gradation and affinity, become elements in the idea of organic creation. It must be seen that the whole phenomena thus pass into strong analogy with those attending the production of the individual organism.'

This last sentence leads us to the special theory proposed by the author to account for the existence of the present forms of life. This theory, termed by the writer the theory of 'progressive development,' may be stated in his own words.

'The several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the providence of God, the results, first, of an impulse which has been imparted to the forms of life, advancing them in definite times by generation through grades of organisation terminating in the highest dicotyledons and Vertebrata, these grades being few in number and generally marked by intervals of organic character which we find to be a practical difficulty in ascertaining affinities; second, of another impulse connected with the vital forces, tending in the course of generations to modify organic structures in accordance with external circumstances, as food, the nature of the habitat, and the meteoric agencies, these being the 'adaptations' of the natural theologian. We may contemplate these phenomena as ordained to take place in every situation and at every time where and when the requisite conditions are presented-in other orbs as well as in this in any geographical area of this globe which may at any time arise-observing only the variations due to difference of materials and of conditions.'

R

Put briefly, the theory of progressive development is that the primitive cells, which constituted on this hypothesis the original forms of life, and which had been presumably produced by spontaneous generation, were advanced through a succession of higher grades and a variety of modifications,' in obedience to some law of an absolute nature, the whole process being analogous to the embryonic development of an individual animal. Just as each individual animal passes through a series of changes during the course of its development— these changes taking place in a fixed order-so the writer of the 'Vestiges' supposes that the primordial forms of life also passed through a series of developmental changes, the different stages of their development being represented by the life-assemblages of the successive great geological periods. These developmental changes are supposed to have taken place in a fixed order, and to have been progressive in character; and the present forms of life are supposed to represent the final term in the developmental cycle of these hypothetical primordial cells. It is not necessary to enter here into any discussion of the theory of progressive development. The obvious objection that an evolutionist of the Spencerian school would take to it is that, from his point of view, 'the impulse which has been imparted to the forms of life,' and to which their subsequent progressive development is supposed to be due, is a mere metaphysical conception, a hypothetical and scientifically inadmissible agency.

THE THEORY OF NATURAL SELECTION.

CHARLES DARWIN.

IT remains to consider very briefly the leading points involved in the theory of the Origin of Species by means of Natural Selection,' which the world owes to the genius of Charles Darwin, and by which the entire science of zoology has been fundamentally altered. There is, indeed, no revolution so great as that effected by the introduction of a new principle; since that involves a reconstruction from the foundation upwards, and implies a much more serious change than the mere putting on of a roof, or the addition of a buttress or of any sort of pendicle, however important such may be in itself. Darwin, however, introduced a introduced a novel principle into biology; and in so doing he profoundly altered the entire attitude of naturalists and botanists towards the world of living beings. Moreover, when the organic world came to be viewed in the light of this new principle, it became at once evident that its complexities depended, to a large extent at any rate, upon causes which are open to our investigation, and are not wholly

beyond our comprehension. The theory of the origin of species by special creation laboured under the inevitable defect that it 'closed the record,' and in many directions shut the door to further research. The theory of the origin of species by means of natural selection has not only brought to light a whole series of problems, many of which are of a most far-reaching character, but it has solved some of them, and has pointed out to us the way in which others may yet be solved at some future date.

As has been seen, the theory that the present state of the natural world was the result of its evolution from a former state did not originate with Darwin. Like others of the profoundest conceptions of the human mind, it had been more or less clearly recognised by more than one earlier philosopher, and notably by Erasmus Darwin and Lamarck. The theory that the 'species' of animals and plants now in existence had been produced by the modification of pre-existing forms of life, and that species were therefore not immutable, also did not originate with Darwin. Lamarck had definitely promulgated this theory, and other writerssuch as Erasmus Darwin and Goethe-in the early part of this century or the close of the last, had put forth similar ideas. Lamarck's views, however, had remained little more than a barren speculation-unheeded by most, and scoffed at by many-and no change had been produced in the generally accepted views as to the nature of 'species' by the publication of the 'Philosophie Zoologique.' To Darwin is incontestably due the pre-eminent merit of having established a theory which