so soon as that mistake was seen the difficulty vanished.

Lord Salisbury also brought forward the further objection that physicists had shown that the earth had not existed long enough to allow of the process of development by the Darwinian theory, as that process was necessarily a very slow one. This also is a misconception of Darwinism. The objection is a mild form of the very venerable one which Cuvier brought against the theory of Lamarck in the beginning of the century, and which is mentioned in the first of these lectures. The answer is that if organic development has been slow during the last three or four thousand years, so also has been geological development. As the earth has, as a matter of fact, existed long enough for the geological evolution to work out, so also must it have existed long enough for the organic evolution; for all through the earth's history the two have gone together. From the Radiolarians and sponges of the Huronian, through the Trilobites and Brachiopods of the older Palæozoic, the fishes and land plants of the newer Palæozoic, the reptiles and Gymnosperms of the Mesozoic, the birds, mammals, and angiosperms of the Cainozoic, the geologic and biologic evolutions have marched hand in hand; and as

there has been time for one there must have been time for the other. The rate of evolution does not affect Darwinism, which has nothing to do with the origin of varieties. If the varieties came quickly, natural selection would act quickly; and vice versa. No doubt, if the physicists are right, variation must have gone on quicker than it does now; but Professor Poulton has shown that the data on which physicists have calculated the short history of the earth are untrustworthy, and not entitled to so much weight as the facts brought forward by geologists.'

Of course we do not expect Lord Salisbury to be up-to-date in biological theory; but as his address will probably be memorable as the last attack on Darwinism from the Presidential Chair of a scientific society, and as it contains what he evidently thought was a death-blow to the whole theory, I feel obliged to mention it here.

The first thing to do, in order to understand Darwinism, either old or new, is to dismiss from our minds any idea that it goes to the root of things and attempts to explain origins. The truth is that the new Darwinism is merely an expanded form of the old, in which, in addition to selection, isolation is shown to be necessary for 'British Association Report for 1896, p. 808.

organic evolution; and this, in my opinion, is the only real advance that has been made since Darwin's death. The new teaching explains the facts much better than the old; but there still remains much to be desired, especially in the collection of evidence to test the truth of those parts of the theory which relate to physiological isolation.

IDEA OF AN INTERNAL TENDENCY TO PRO

GRESSION

It will be noticed that in the first lecture it is pointed out that natural selection does not afford a complete solution of the problem of organic evolution; but the new teaching is not even mentioned for, plain as it now seems, it was not very convincing in its early days. On the contrary, it is there stated that " many biologists are of opinion that there is an inherent tendency towards higher organisation; they think that protoplasm tends to become more and more complex, and that evolution is the inevitable outcome of a fundamental property of living matter." The idea of an internal force, compelling development in certain directions, and especially towards higher organisation, which was common eleven. years ago, is still held by some naturalists; but it has almost vanished before the accumulating

testimony of paleontology, that several of the lower organisms have existed from the earliest part of the Paleozoic era up to the present day, without undergoing any important change in their hard parts-which alone have been preserved-and therefore probably without much change in their soft parts either. Indeed, most of the classes of animals and plants have undergone but little change since their first appearance. In comparatively few cases has change been rapid; but it is these rapidly changing forms which seem so remarkable in our eyes, and give the impression that great change is more universal than it really is. Except the large Lycopods and Crustaceans of the newer Palæozoic, the reptiles and birds of the Mesozoic, and perhaps a few of the Eocene hoofed mammals, there is nothing among extinct plants and animals that would appeal to the untrained eye as anything remarkable and unlike living plants and animals. Our views on this subject are much exaggerated, owing to the numerous drawings and models that have been made of a few of the most extraordinary of the animals; and we forget that they were only a few among a host of quite ordinary beings.

DEFINITE AND INDEFINITE VARIATION

In the second lecture I have entered somewhat fully into the difference between Lamarckism and Darwinism, because I have noticed misconceptions on the subject among several writers on evolution; and it was necessary to make the difference as clear as possible, without going into technical details. There seems to be especial confusion on the subject of definite or determinate, and indefinite or indeterminate variation; and a few more words about it may not be out of place in this Introduction; for, although not included in Darwinism, it has an indirect bearing on our views of natural selection.

Some writers seem to think that because determinate variation implies a directing agency, therefore indeterminate variation can have no directing agency, and that it has no cause at all. This confusion is largely due to the unfortunate substitution of the terms "determinate" and "indeterminate" for Darwin's I definite" and "indefinite" variation, which are far more appropriate. I have also seen it stated that, if variations are definite, there is nothing left for natural selection to do; which is quite a mistake. A definite variation may be injurious, or it may be