one of the most acute of men and a great reader of natural history, speaks, in his Queen of the Air, as if Darwinians held that a bird could develop from a fish. The bird is separated from the fish by the entire family of reptiles, and a Darwinian feels, more intensely than a naturalist of any other school can feel, that the overleaping of this enormous gap is an impossibility in the nature of things. He does not recognise, throughout the vast series, one instance of "overleaping.' He maintains that the evolution took place by means of infinite gradations and countless variations, each so minute as to be hardly observable. His real difficulty is not to account for such differences as those between a salmon and an elephant-a difficulty which no one whose knowledge of science exceeds that of a popular jester or an Athenæum reviewer would propose-but to find explicit proof that any one well-defined species, such as the missel-thrush, sprang by ordinary generation and natural selection from any closely-allied species, such as the common thrush or blackbird. This difficulty is well and honestly put by Professor Huxley. "After much consideration," he writes-at least he wrote this eleven years ago, and I am not aware that he has retracted it-" After much consideration, and with assuredly no bias against Mr. Darwin's views, it is our clear conviction that, as the evidence stands, it is not absolutely proven that a group of animals, having all the characteristics exhibited by species, has ever been originated by selection, whether artificial or natural. Groups having the morphological character of species, distinct and permanent races, in fact, have been so produced over and over again; but there is no positive evidence, at present, that any group of animals has, by variation and selective breeding, given rise to another group which was even in the least degree infertile from the first. Mr. Darwin is perfectly aware of this weak point, and brings forward a multitude of

ingenious and important arguments to diminish the force of the objection. We admit the value of these arguments to their fullest extent-nay, we will go so far as to express our belief that experiments conducted by a skilful physiologist would very probably obtain the desired production of mutually more or less infertile breeds from a common stock, in a comparatively few years; but still, as the case stands at present, this little rift within the lute' is not to be disguised nor overlooked." Mr. Alfred Russell Wallace has mentioned some facts which bear directly on this difficulty. In certain districts lying widely apart from each other in South America he found butterflies which, though closely-allied species, had the characteristic specified by Professor Huxley, that they were mutually infertile. But in the districts between their respective localities there were several varieties intermediate between these two, and with these the species at, so to speak, each end of the line, were fertile. Under these circumstances it is easy to see that two species, which mutually repelled each other and were infertile, might be connected by ties of relationship through varieties intermediate between them. The passage I have quoted from Professor Huxley, and this illustration from Mr. Wallace, enable us to realise how exquisitely slight is the dividing line across which sound Darwinians believe it to be possible for one species to pass into another.

1. Mr. Darwin maintains that this barrier has been passed in a continuous series for millions of years, and that thus the countless varieties of the animal world have arisen. Yet, notwithstanding the array of evidence in favour of this conclusion, there is a prevalent misconception that Darwinism is a mere dream, an idle fancy, a baseless speculation, having no facts in its favour. But the facts which point

1 Lay Sermons, Addresses, and Reviews. By T. H. Huxley, 1870. p. 323-4.

towards Darwinism are numerous and significant. Students in natural history had observed these facts long before Mr. Darwin's day, and had to some extent formed theories to account for them. It was the existence of these facts in botany and zoology that first led Mr. Darwin to his famous theory. 2

It is hardly possible to put into a brief paper arguments which shall be deemed decisive in favour of the general doctrine of Darwinism; the force of the appeal which the process of reasoning makes depends so largely upon a somewhat wide acquaintance with the facts of natural history and geology, and upon the habit of mind which is formed by the constant recognition of facts which tend with more or less of directness to the same conclusion. Two or three lines of the argument may, however, be indicated.

There is, first of all, the discovery which every student of botany or zoology is continually making, that forms which his manuals teach him to regard as specifically distinct are linked together by varieties which he cannot rank with confidence in this or that class, but which rather seem as stepping-stones between classes. The first idea suggested to him is that of a "rectification of boundaries; " the increase or the diminution of species so that his varieties may find their proper resting-place. The study of teratology may for a time confirm him in this belief. He finds, for instance, that variations within species may be produced by an excess or by a lack of nourishment; and that when the conditions are equalised the varieties disappear. But there are variations

2 But the theory of natural selection was first announced by Lamarck, in the year of Mr. Darwin's birth, in 1809; while Leopold Von Buch, in 1825, Geoffrey St. Hilaire and Von Baer in 1823, Oken in 1842, Mr. Herbert Spencer in 1852, and Mr. Alfred Russell Wallace in 1858, are the more prominent thinkers among many who had discussed natural selection in plants and animals since Lamarck announced the idea, and before Mr. Darwin published the Origin of Species.

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which refuse to vanish; there is a law of persistence of type which frequently comes into operation here. Gardeners are aware of "sports" in vegetation. One branch of a rose or of a fruit-tree will produce different flowers or fruits from the rest, and buds taken from this branch will keep the character of the "sport" under different conditions of culture, and the sport" may become the parent of a new variety. The Saxifraga cernua is thought by some botanists to be only a variety of the meadow saxifrage; but it clings to its Alpine home, and maintains its characteristics there. It refuses to be cultivated back again into Saxifraga granulata. Let the young student, then, conceive of an accumulation of various conditions, all working in one and the same direction. His knowledge that if there are varieties that tend to revert to a common form, there are also types that are persistent, forms that will keep the variation and die in altered conditions rather than revert, will prepare him to welcome in the Darwinian doctrine of the evolution of species a plausible solution of his problem.

The possibility of accumulating variations in a given direction is a fact familiar to the agriculturist. The whole art of cultivation and the skill of the breeder depend upon it. The ferns, flowers, and fruits of our gardens, so far as these have been improved by culture, have been improved in this way. In this way have come the race-horse and the Leicestershire sheep. There is a power in nature by which some variations. are perpetuated and accumulated, and others are dropped. For since every variation, however slight, and whatever function it affects, is either an advantage or a disadvantage to its possessor; in the struggle for existence arising from the fact that all living forms multiply faster than their means of subsistence, the favoured individuals will survive, while the others will die out. This is the theory of natural selection. The struggle for existence tends constantly to exaggerate any

slight advantage an individual may have over its fellows; and the accumulation of variations is still further aided in the case of animals by the law of sexual selection, the preference which the females show for those males in which certain qualities are predominant.

The study of palæontology extends immensely the scope of this argument. It supplies links between species and genera the existing forms of which are widely separated, and as in the exposition of the pedigree of the horse, for instance, which is the subject of one of Professor Huxley's popular lectures, it marks the different stages in the development of particular organs. The geological record, both in the hints it furnishes and in the imperfection of its testimony, may be compared to the ruins of castles and cathedrals which supply data for the conclusions of the archeologist. One pretty complete ruin gives the architect confidence in his interpretation of many scattered fragments; and when fossil remains are found linking together two or three genera, the paleontologist is aided in his reconstruction of the whole order.

The existence of rudimentary or aborted organs is another strong argument in favour of the doctrine of evolution. Rudimentary legs, for instance, are found under the skin of many snakes; manifestly of no use to them, but intelligible if we may suppose that snakes have descended from walking reptiles. This is but one illustration from a multitude that might be quoted from all departments of life; and their application to the argument depends on our belief that nature cannot lie. These organs must at some time or other have been of use; they are like the characteristic ornaments of Doric architecture, giving us a history of the development from wooden to stone structures. Some philosophers have affirmed that these organs serve to indicate the development of the idea; that though they are of no use to the creature, they serve to mark out the place of the creature in the scale of