primary placental and implacental mammals, and perhaps also for the divergence of the most ancient stock of these and of the monotremes, for in all these cases modifications of structure appear to increase in complexity in at least that ratio. Finally, a vast period must be granted for the development of the lowest mammalian type from the primitive stock of the whole vertebrate sub-kingdom. Supposing this primitive stock to have arisen directly from a very lowly-organized animal indeed (such as a nematoid worm, or an ascidian, or a jelly-fish), yet it is not easy to believe that less than two thousand million years would be required for the totality of animal development by no other means than minute, fortuitous, occasional, and intermitting variations in all conceivable directions. If this be even an approximation to the truth, then there seem to be strong reasons for believing that geological time is not sufficient for such a process.

The second question is, whether there has been time enough for the deposition of the strata which must have been deposited, if all organic forms have been evolved according to the Darwinian theory?

Now this may at first seem a question for geologists only, but, in fact, in this matter geology. must in some respects rather take its time from zoology than the reverse; for if Mr. Darwin's theory be true, past time, down to the deposition of the Upper Silurian strata, can have been but a very small fraction of that during which strata have been deposited. For when those Upper Silurian strata were formed, organic evolution had already run a great part of its course, perhaps the longest, slowest, and most difficult part of that course.

At that ancient epoch, not only were the vertebrate, molluscous, and arthropod types distinctly and clearly differentiated, but highly-developed forms had been produced in each of these sub-kingdoms. Thus in the Verte

brata there were fishes not belonging to the lowest but to the very highest groups which are known to have ever been developed, namely, the Elasmobranchs (the highly-organized sharks and rays), and the Ganoids, a group now poorly represented, but for which the sturgeon may stand as a type, and which in many important respects more nearly resemble higher Vertebrata than do the ordinary or

osseous fishes. Fishes in which the ventral fins are placed in front of the pectoral ones (i.e., jugular fishes) have been generally considered to be comparatively modern forms. But Prof. Huxley has kindly informed me that he has discovered a jugular fish in the Permian deposits.

Among the molluscous animals we have members of the very highest known class, namely, the Cephalopods, or cuttle-fish class; and among articulated animals we find Trilobites and Eurypterida, which do not belong to any

incipient worm-like group, but are distinctly differentiated Crustacea of no low form.

We have in all these animal types nervous systems differentiated on distinctly different patterns, fully-formed organs of circulation, digestion, excretion, and generation, complexly-constructed eyes and other sense organs; in fact, all the most elaborate and complete animal structures built up, and not only once, for in the fishes and mollusca we have (as described in the third chapter of this work) the coincidence of the independently-developed organs of sense attaining a nearly similar complexity in two quite distinct forms. If, then, so small an advance has been made in fishes, mollusks, and anthropods, since the Upper Silurian deposits, it will probably be within the mark to consider that the period before those deposits (during which all these organs would, on the Darwinian theory, have slowly built up their different perfections and complexities) occupied time at least a hundredfold greater.

Now it will be a moderate computation to allow 25,000,000 years for the deposition of the strata down to and including the Upper Silurian. If, then, the evolutionary work done during this deposition only represents a hundredth part of the sum total, we shall require 2,500,000,000 (two thousand five hundred million) years for the complete development of the whole animal kingdom to its present state. Even one-quarter of this, however, would far exceed the time which physics and astronomy seem able to allow for the completion of the process.

17

Finally, a difficulty exists as to the reason of the absence of rich fossiliferous deposits in the oldest strata— if life was then as abundant and varied as, on the Darwinian theory, it must have been. Mr. Darwin himself admits "the case at present must remain inexplicable; and may be truly urged as a valid argument against the views" I entertained in his book.

17"Origin of Species," 5th edit., p. 381.

Thus, then, we find a wonderful (and, on Darwinian principles, an all but inexplicable) absence of minutely transitional forms. All the most marked groups, bats, pterodactyls, chelonians, ichthyosauria, anoura, etc., appear at once upon the scene. Even the horse, the animal whose pedigree has been probably best preserved, affords no conclusive evidence of specific origin by infinitesimal, fortuitous variations; while some forms, as the labyrinthodonts and trilobites, which seemed to exhibit gradual change, are shown by further investigation to do nothing of the sort. As regards the time required for evolution (whether estimated by the probably minimum period required for organic change, or for the deposition of strata which accompanied that change), reasons have been suggested why it is likely that the past history of the earth does not supply us with enough: First, because of the prodigious increase in the importance and number of differences and modifications which we meet with as we traverse successively greater and more primary zoological groups; and, secondly, because of the vast series of strata necessarily deposited if the period since the Lower Silurian marks but a small fraction of the period of organic evolution. Finally, the absence or rarity of fossils in the oldest rocks is a point at present inexplicable, and not to be forgotten or neglected.

Now all these difficulties are avoided if we admit that new forms of animal life of all degrees of complexity appear from time to time with comparative suddenness, being evolved according to laws in part depending on surrounding conditions, in part internal-similar to the way in which crystals (and, perhaps from recent researches, the lowest forms of life) build themselves up according to the internal laws of their component substance, and in harmony and correspondence with all environing influences and conditions.

CHAPTER VII.

SPECIES AND SPACE.

The Geographical Distribution of Animals presents Difficulties.-These not insurmountable in themselves; harmonize with other Difficulties.-Fresh-water Fishes.-Forms common to Africa and India; to Africa and South America ; to China and Australia; to North America and China; to New Zealand and South America; to South America and Tasmania; to South America and Australia.-Pleurodont Lizards.-Insectivorous Mammals. Similarity of European and South American Frogs.-Analogy between European Salmon and Fishes of New Zealand, etc.-An Ancient Antarctic Continent probable.Other Modes of accounting for Facts of Distribution.-Independent Origin of Closely-similar Forms.-Conclusion.

THE study of the distribution of animals over the earth's surface presents us with many facts having certain not unimportant bearings on the question of specific origin. Among these are instances which, at least at first sight, appear to conflict with the Darwinian theory of "Natural Selection." It is not, however, here contended that such facts do by any means constitute by themselves obstacles which cannot be got over. Indeed, it would be difficult to imagine any obstacles of the kind which could not be surmounted by an indefinite number of terrestrial modifications of surface-submergences and emergences-junctions and separations of continents in all directions and combinations of any desired degree of frequency. All this being supplemented by the intercalation of armies of enemies, multitudes of ancestors of all kinds, and myriads of connecting forms, whose raison d'être may be simply their utility or necessity for the support of the theory of "Natural Selection."