very slowly. Whether these strata were deposited slowly or less slowly, we know that the forms of life changed at the same rate. "Biology takes her time from geology. The only reason we have for believing in the slow rate of change in living forms is the fact that they persist through a series of deposits which, geology informs us, have taken a long while to make. If the geological clock is wrong, all the naturalist will have to do is to modify his notion of the rapidity of change accordingly; and I venture to point out that, when we are told that the limitation of the period during which living beings have inhabited this planet to one, two, or three hundred million years requires a complete revolution in geological speculation, the _onus probandi_ rests on the maker of the assertion, who brings forward not a shadow of evidence in its support." Perhaps, although this is now an old controversy, it is worth while to recall that the keenness of Huxley's language was not directed against Sir William Thomson, between whom and Huxley there was no more than the desire to argue out an interesting scientific question upon which their conclusions differed, but between Huxley and those outsiders who were always ready to turn any dubious question in science into an argument discrediting the general conclusions of science. The last time that Huxley occupied the Presidential Chair of the Geological Society was in 1870, and he occupied his Presidential address by a review of the "old judgments" which he had given in the course of his first address in 1862. The address was entitled "Palæontology and Evolution," and the most important part of it was a complete withdrawal of the fears he had expressed that geology would not supply definite evidence of the transformation of species. Important discoveries had come thick and fast; and, at least in the case of the higher vertebrates, he declared that, however one might "sift and criticise them," they left a clear balance in favour of the doctrine of the evolution of living forms one from another. But, with his usual critical spirit, examining arguments that bore against a conclusion for which he hoped almost more stringently than arguments apparently favourable to what he expected to be true, Huxley made an important distinction, the value of which becomes more and more apparent as time goes on. In the first flush of enthusiasm for Darwinism, zoölogists and palæontologists allowed their zeal to outrun discretion in the formation of family trees. They examined large series of living or extinct creatures, and so soon as they found gradations of structure present, they arranged their specimens in a linear series, from the simplest to the most complex, and declared that the arrangement was a representation of the family tree. The fact that the line of descent apparently could have followed along the