THE “ Evolution of Life,” by Dr. Henry T. Chapman, is a brief summary of the evidences of what is currently known as the Darwinian theory ; and it is, likewise, so far as we know, the first attempt to place before the English reader, in connected shape, the results of Professor Haeckel’s inquiries and speculations. The book is, indeed, to such an extent the mere reproduction of Haeckel’s “ Schöpfungsgeschichte,” that, if the latter work had ever been rendered into English, the present work would have had no raison d'être at all. For, in passing through Dr. Chapman’s mind, the theories of Haeckel have not undergone any further elaboration, — not even that kind of elaboration which would have been implied in the terse and condensed presenting of them. They are simply repeated, in a curtailed and fragmentary sort of way, as naturally results from the attempt to bring into a book of 180 pages the substance of a book five times as large. Nor can it be said that Dr. Chapman’s style of exposition is such as to render more intelligible or more attractive the doctrines which he sets forth. We do not mean to imply that his sentences are ambiguous or obscure ; certainly no one at all familiar with the subject can find any difficulty in following his exposition or in estimating the bearings of his arguments. But the “general reader” — that terrible bugbear which scientific writers profess to be so desirous of propitiating—will certainly be repelled by the pitiless way in which Dr. Chapman sets out to drag him into the midst of intricate mooted questions in comparative anatomy and classification ; and he must often be puzzled, not to say bewildered, by the suddenness with which one line of argument is dropped and another taken up. For example, the subjects of the ability of natural selection to work deep-seated variations, of the pairing of hybrids, of transitional varieties, of the duration of geologic time, of the acquirement of instincts and a priori ideas through inherited modifications of the nervous system, and of the development of complex organs, like the eye and ear, are all treated within the compass of three pages (157 — 160) ; so that, just as the reader’s mind has become prepared to follow the further discussion of the question in hand, it is forthwith dropped, and a fresh question taken up.
Though not strikingly original, nor attractive, nor sufficiently thorough, Dr. Chapman’s book is, however, by no means devoid of interest and value. Though we fear that the author will be disappointed in the expectation held out in the Preface, that much of the current misapprehension concerning the Darwinian theory will be cleared up by his book, there are nevertheless many persons, already somewhat familiar with natural history and the doctrine of evolution, who will find here much that is serviceable. Especially good are the genealogical tables of the animal and vegetal kingdoms, though they would have been more instructive if thrown into the form of family trees, as in the plates at the end of Haeckel’s “ Generelle Morphologie.” In the absence of any translation of the lastnamed colossal work, or of its lesser companion, the “ Schöpfungsgeschichte,” it is a good thing to have presented in English the main outlines of Haeckel’s classification. The sections on classification are the most satisfactory in the book. The author follows Haeckel in erecting a third kingdom, called protists, comprising such organisms as are neither distinctively animal nor vegetable ; an arrangement which many naturalists condemn, but for which there is much to be said, provided no attempt be made to draw a hard and fast line between the protistic and the two higher kingdoms ; and no follower of Haeckel is likely to make such an attempt. Since a gregarina or a bacterium is certainly not an animal, and certainly not a vegetable, while it is certainly a living thing, there would seem to be great convenience in having a region to which to assign it; though this “ region ” of protists, or lowest organisms, be not strictly a “kingdom,” but rather the border-land between the animal and vegeable worlds on the one hand and the realm of inorganic existence on the other.
The old Cuvierian sub-kingdom of Badiata is broken up, as it ought to be, since it was merely a provisional grouping of all such animal forms as are neither Vertebrata, Annulosa, nor Mollusca, and thus brought together forms so utterly different as corals and star-fishes, Of the organisms which composed it, the infusoria are transferred to the kingdom of Protists, the echinoderms form a sub-kingdom by themselves, leaving for the lowest animal sub-kingdom the Cœlenterata, comprising on the one hand the actinozoa, represented by the anemones and corals, and on the other hand the hydrozoa, represented by the jelly-fish. Haeckel’s views concerning the origin of the true radiate type, as exemplified in the echinoderms, are very interesting, and are strikingly similar to Mr. Spencer’s explanation of the origin of the annulose type already commented on in these columns. First let us note that just above the cœlenterata, though not necessarily derived from any known forms of them, comes the group of Worms, —a feature of the old Linnæan classification revived. Whether it be regarded as a true sub-kingdom or not, — and it is in harmony with the doctrine of evolution that such a point should be difficult to settle,—it appears indubitable that the group of worms forms, as it were, the foundation for the four great groups, echinoderms, articulata, mollusca, and vertebrata. We have elsewhere (May, 1872,) remarked upon the probability that the annulose animal is originally a colony of little spheroidal animals, the coalescence being explicable as a case of arrested reproduction by spontaneous fission. In similar wise, Haeckel supposes the true radiate type, as exemplified in the star-fish, to have been formed by the coalescence of five worms. An analogous case is that of Botryllus, which is made up of many little ascidians ; and, as Dr. Chapman observes, “ there is nothing more extraordinary in five worms living together as a [primeval] star-fish.” Embryology favors this view. “ The egg of the star-fish is transformed into a larva, provided with an intestine from the inner part of the body of the larva. Around its mouth appear five distinct layers, which, uniting at their posterior ends, form the body and arms of the mature animal. The same kind of reproduction is seen in the Sipunculi, which are supposed to be indirectly the ancestors of the starfish, and also in the Nemertian worms from which, or their allies, the Sipunculi and other articulated worms have descended. Within a few years there have been found a very well-preserved group of fossil worms, — the Phractelminthes, or mailed worms. These are considered by Haeckel to be intermediate between the Sipunculus and the star-fish, they being scarcely distinguishable from the arms of the latter. Through the union of worms like the Phractelminthes have the star-fishes been produced. The origin of the star-fishes from the worms is in perfect harmony with the structure, development, and petrified remains of the group. The most striking facts of their economy are explainable on such a theory, but arc perfectly meaningless on any other. The star-fishes are probably the ancestors of the remaining echinodermata.”
While the union of primeval worms into this radiated structure has been productive of comparatively few forms of life, the longitudinal coalescence, on the other hand, has given rise to the great sub-kingdom of the articulata, numbering, in the insects alone, a greater variety of forms than is to be found in all the remainder of the animal world taken together. As a third and totally different offshoot from the group of worms, we have the Bryozoa, leading us up to the sub-kingdom of molluscs, and the Tunicata, an aberrant molluscoid type, of surpassing interest, from its close relationship to the lowest forms of vertebrate life. Kovalevski’s important discovery of the correspondences in embryonic development between the ascidian and the amphioxus, or lowest surviving vertebrate, is well described by Dr. Chapman, who, here as elsewhere, closely follows Haeckel. Here the most considerable of all the “missing links,” directly connecting the vertebrated animal with a lowly form rooted plant-like to the earth, has at last been found.
Passing over many interesting points, until we come to the classification of mammals, it is to be observed that Dr. Chapman, differing in this instance — though, we think, unfortunately — from Haeckel, is inclined to derive the existing orders of monodelphians from various corresponding orders or pseudo-orders of didelphians ; that is, the monkeys from a marsupial like the opossum, the ungulates from a marsupial like the kangaroo, the carnivora from a wolf-like marsupial, etc. On this view, we have to suppose that a great variety of animals, scattered all over the earth, have agreed in losing the pouch and in acquiring a placenta; while on the common view, that all monodelphians are the divergent progeny of some one didelphian, like the opossum, we have to suppose that exposure to similar physical conditions has caused several orders of monodelphians to undergo changes like those previously experienced by didelphians. And this is unquestionably the more probable supposition.
One of Haeckel’s chief faults is his positiveness. In his most praiseworthy effort to trace the pedigree of man even back to the congeners of the ascidian, he is not content with stopping short of telling us, at each step, that we have den sicheren Beweis, “ the sure proof,” of the proceeding. We are strongly inclined to suspect that in no case have we as yet obtained “ sure proof,” save in the classification of man with the Catarrhinae, and in the indication of a proximity between the amphioxus and the ascidians. Undoubtedly our grandchildren will be able to point out many cases in which our scrutiny of the forms of animal life has been faulty. So, also, with regard to the submerged continent of “ Lemuria,” where, as Haeckel and Dr. Chapman think, the human race had its origin, we ought to be content to admit that we know next to nothing. That a continent has existed, connecting Madagascar with Sumatra and Java, seems to be quite probable ; and it is not at all improbable that, if we could explore that submerged land, we might find traces of the earliest type of simioid man. But dogmatic statements on such a point are at present as absurd as they are unneeded.
Professor Tyndall’s little book on the “ Forms of Water in Clouds and Rivers, Ice and Glaciers,” has just appeared, being the first volume of that “ International Scientific Series ” for which we are indebted to the zeal and energy of Dr. Youmans, It is a charming little book, pleasant for learned and unlearned readers alike. If this is a fair specimen of the series which is to follow, Dr. Youmans will indeed be entitled to the gratitude of the four or five nations which share in the benefits of the undertaking. The next volume — “ Physics and Politics,” by Mr. Bagehot — is, not only a charming book, but a book rich in original thought, judging from the fragments we have seen ; and when it appears we hope to call attention to some of the questions raised in it.
The Lowell Institute has seldom been so crowded as on the evenings of Professor Tyndall’s lectures, and seldom has a Boston audience witnessed neater or more satisfactory experimentation. The manner of the lecturer, barring some slight nervousness, was agreeable ; and the lectures were elementary (not to say rudimentary) enough in style and matter to satisfy even those who are most afraid of approaching abstruse subjects. One would suppose it difficult for any one to have heard the second lecture and not remember forever after what spectrum analysis means. There is one point, however, in which Professor Tyndall’s usual explicitness seems to fail him, because, as we think, it is a subject on which one cannot attain the distinctness of conception upon which explicitness of expression depends. We refer to the hypothesis of a universal ether in which the molecules of all bodies float as in a boundless sea, the waves of which constitute heat, light, or actinism. The existence of such an ether is by many persons supposed to be a necessary postulate of the wave theory of light and heat ; but so far is this from being true, that, not only Euler, one of the founders of the undulatory theory, but Mr. Grove, the greatest living English physicist, has rejected the hypothesis as a quite unnecessary encumbrance. We do not purpose here to enter into a discussion of the matter. But we do not think Professor Tyndall could possibly be better employed than in giving a course of lectures on the ether-hypothesis, in which, after rigorously defining the ether by its physical attributes, he should proceed to explain the known phenomena of undulation, without once (if we may be allowed the best expression for it) “going back on” his definition. We do not say it cannot be done. We do not know positively that it has not been done. But we should very much like to see it done.