I have no space to go into the evidence of similar "missing links" which have been recently supplied by palaeontological researches in the case of several other groups of animals; but their consideration seems to me quite to justify a more recent utterance of Professor Huxley, who, in 1878, wrote in the _Encyclopaedia Britannica:_ "On the evidence of palaeontology, the evolution of many existing forms of animal life from their predecessors is no longer an hypothesis, but an historical fact; it is only the nature of the physiological factors to which that evolution is due which is still open to discussion." III. THE ARGUMENT FROM GEOLOGY. But this allusion to fossils leads me to the next division of my subject--the argument from geology. It is not, however, necessary to say much on this head, for the simple reason that the whole body of geological evidence is for the most part of one kind, which although of a very massive, is of a very simple character. That is to say, apart from the increasingly numerous cases, such as the one just mentioned, which geology supplies of extinct "intermediate links" between _particular_ species now living, the great weight of the geological evidence consists in the _general_ fact, that of all the thousands of specific forms of life which palaeontology reveals to us as having lived on this planet in times past, there is no instance of a highly organised form occurring low down in the geological series.[1] On the contrary, there is the best evidence to show that since the first dawn of life in the occurrence of the simplest organisms, until the meridian splendour of life as now we see it, gradual advance from the general to the special--from the low to the high, from the few and simple to the many and complex--has been the law of organic nature. And of course it is needless to say that this is precisely the law to which the process of descent with adaptive modification would of necessity give rise. [1] Some of the lower vertebrata (Elasmobranch and Ganoid fishes) occur, indeed, in early strata (upper Silurian); but still far from the earliest in which some of the invertebrata are found. The general statement in the text applies chiefly to the more highly organised forms of the vertebrate series. IV. THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION.