Puslapio vaizdai

nor of the Cartilaginous fishes, but altogether analogous to the Bichir and the Lepidosteus. So that these two genera, apparently mere exceptions in the present creation, in reality constitute a type by themselves, which, though not numerous at present, is, nevertheless, the expression of an entire order of things. Associating with these fishes the numerous fossil species whose scales have the same structure, Mr. Agassiz made his division of Ganoïdians, which already contains many hundred species, and promises to become still larger, since it predominates in all the formations anterior to the chalk. Mr. Agassiz recognizes several distinct families of this order; the two principal ones are the Sauroïdians, to which the Lepidosteus and the Bichir belong; and the Lepidoïdians, which were inoffensive and probably omnivorous fishes, somewhat resembling the Carp in appearance, but having no representatives in the present creation.

These researches among the fossils had not a geological interest alone. The numerous examinations that Mr. Agassiz was obliged to make, in order to establish in all points the analogy of extinct species with living types, revealed to him anatomical relations of great interest, which had been hitherto passed over. He thus discovered the important fact, not before made known, that there exists a remarkable parallelism between the development of the individual, and the development of the whole class in the series of ages. In the early stages of embryonic life, the vertebral column does not exist. In place of it there is found, in the embryo, a gelatinous mass, called the dorsal cord. Around this cord (which remains for a longer or shorter time in all fishes,) are formed the vertebræ, as bony rings. These rings gradually increase, and encroach more and more upon the dorsal cord, which, in most fishes, at last disappears. In some types, however, for example, in the Sturgeon, it remains during the whole life; so that this fish has no vertebræ, and the apophyses rest immediately on the dorsal cord. Now, Agassiz shows us that this is the case with all the fishes of former epochs. They all have distinct spinous apophyses, often very strong and completely ossified, but they show no trace of separate vertebræ ; whence he concludes, that these organs were wanting, and that the dorsal cord continued throughout life, as in the Sturgeon. As to the relative superiority of living types, also, embryology reveals to us a wonderful parallelism. There is no fish, however imperfect, whose organization does not corre

spond to some phase in the life of more perfect types. Take, for example, the Lamprey, or that still more imperfect fish known under the name of Amphioxus, or Branchiostoma, which Pallas placed among the Snails, from its great dissimilarity to ordinary fishes. The former has, in place of the cranium, only a cartilage corresponding to the base of the skull; and the latter is deprived even of this, and the dorsal cord extends to the end of the snout. The first has a single fin, more or less divided; in the other, the fin extends along the whole body. Finally, neither has jaws, properly so called. Now, the most perfect of our fishes, such, for example, as the Salmon, are all, at one period of their life, at the same point of development, but with them it is a transient state, a stage of growth; whilst in the others it is the permanent condition.

These views have a high philosophical bearing, particularly in their application to other classes of the animal kingdom. It is in accordance with them that Agassiz determined the rank to be assigned to the various families of fishes, according to their organization.

It is to Geology, nevertheless, that the greatest profit is derived from these discoveries. In comparing together the fishes found in various formations, Agassiz from the first had also thrown new light on the relative age of these formations. Thus, to cite but a single example, he was enabled by the study of the fishes of the slate of Glaris, to demonstrate that this deposit, which had previously been considered as belonging to the most ancient sedimentary rocks, the grauwacké, is much more recent, and forms a part of the cretaceous group. Another and more general result of his labors was the discovery, that not only are all the fossil species different from those now living, but also, that from one formation to another, the species are equally distinct. And this diversity, according to him, is not confined to the larger formations, but exists equally between the various stages of the same formation. Thus he recognizes no species as common to the lias and the upper Jura limestone; to the upper and lower cretaceous deposits; to the ancient and recent strata of the tertiary formations, &c. The necessary deduction is, that the whole creation has been renewed at different epochs, by a direct intervention of the Creator. Agassiz, however, did not stop here, but pushed his conclusions still further. From the fact that certain basins, like certain regions of the earth's surface, are inhabited by species peculiar to them, not found elsewhere

in deposits of the same age, he inferred that each creation was local, that is to say, that species were created in the localities they inhabit, and that to each was assigned a limit, which it does not pass so long as it remains in its natural condition. Man alone, and those few species that are associated with him, are exceptions to this general law. And as the migrations of even these species takes place under the direct influence of man, we may conclude that they were unknown to former epochs.

These considerations, with others not less important, concerning the relation which this localization bears to the temperature and degree of elevation of continents at different epochs, suggested to Agassiz some general reflections, with which he closes his chapter on Classification, and which we transcribe, as showing the spirit in which this work is written. "Such facts," says he, "loudly proclaim principles which science has hitherto left untouched, but which the researches of paleontology urge upon the observer, with an ever increasing force those, I mean, that respect the relation of the Creator to the universe. We see phenomena closely connected in the order of succession, yet without any sufficient cause within themselves for the connection; an infinite diversity of species, without any material bond of union, so grouped as to present the most admirable progressive development, in which our own species is involved. Have we not here the most incontestable proofs of the existence of a Superior Intelligence, whose power alone has been able to establish such an order of things? The methods of scientific investigation, however, are of such strictness, that what seems to our feelings a matter of course, we cannot admit, unless supported by numerous and well-established facts; on this account, I have delayed expressing my convictions on this subject, until the last moment; not that I have wished to avoid the discussions which the announcement of such results must necessarily excite, but that I have been desirous not to provoke them before establishing for these results a purely scientific foundation, and supporting them by rigid demonstrations, rather than by a profession of faith. An acquaintance with more than fifteen hundred species of fossil fishes, has taught me that species do not pass insensibly into each other, but that they appear and disappear unexpectedly, without showing any immediate connection with those preceding them. For I do not think that any one can seriously affirm that the nu

merous types of Cycloïdians and Ctenoïdians, which are almost contemporaneous, are descended from the Placoïdians and Ganoïdians. This would be, in fact, to say, that Mammalia, and thus man, are directly descended from the fishes. All these species have a fixed time of appearance and disappearance; indeed, their existence is limited to a definite period. Nevertheless, they present, in their general character, affinities more or less close, and a definite coördination in a given system, intimately connected with the mode of life of each type, and even of each species. More than this, in all ages, an invisible thread runs through this immense diversity, presenting to us, as a definite result, a continual progress in this development, of which man is the end, the four classes of vertebrated animals the intermediate steps, and the invertebrata the constant accessory accompaniment. Have we not here the manifestations of a mind as powerful as prolific ?-the acts of an intelligence as sublime as provident?-the marks of goodness as infinite as wise?-the most palpable demonstration of the existence of a personal God, author of all things, ruler of the universe, and dispenser of all good? This at least is what I read in the works of the creation, in contemplating them with a grateful heart. Such feelings, moreover, dispose us better to fathom the truth, and study it for itself; and it is my conviction, that if, in the study of the natural sciences, these questions were less avoided, even in the sphere of direct observation, our progress would be generally more sure and more rapid."

It is not astonishing that such results, accompanied by views so wide, and presented with the irresistible force of a profound conviction, gained for their author the respect of the scientific world. Learned societies vied in showing their sympathy with him; and, (a distinction then unparalleled,) at the age of thirty-four, Agassiz was a member of every scientific academy in Europe.

England was, at that time, in advance of all other nations in the study of Geology. It was here that Agassiz found at once the richest materials and the greatest encouragement. Whole collections were put at his disposal, and he obtained in this manner many precious specimens. Some of his friends recollect with pleasure the impression produced by his visit on the naturalists of the United Kingdom. Several universities were desirous of numbering him among their professors, and the cities of Edinburgh and Dublin, beside conferring on

him the degree of LL. D., enrolled him also among their citizens. We learn that his personal influence induced several persons of high rank to engage in the study of Natural History-among others, Sir Philip Egerton and Lord Enniskillen, whose collections are known to all paleontologists. He became intimate with the most influential persons in the kingdom; he was the welcome guest of Sir Robert Peel and Lord Egerton, and the friend of Buckland, Owen, Murchison, and other distinguished English naturalists.

Having obtained from the study of Fossil Fishes results so important to the history of the development of the whole creation, Agassiz naturally sought to confirm them by the study of other classes of animals, and, accordingly, applied himself to the examination of the Mollusca and the Echinodermata. The latter had been, in general, somewhat neglected by naturalists; the fossil species, in particular, were scarcely known, although, from their great variety, and the complicated structure of their shells, they are of great importance in determining the age of various deposits.

In a short time, he had collected a considerable number of species, belonging to various public and private collections throughout Europe, and in 1836 he published, in the first volume of the Mémoires de la Société des Sciences Naturelles de Neuchâtel, a Prodromus of the class of Echinodermatathe principles of which have since been generally adopted. The same volume contains another paper, giving descriptions and figures of the fossil Echini belonging to the Neocomian group of the Neufchatel Jura. A year afterwards, he published, in another periodical,-(the Mémoires de la Société Helvétique,)-descriptions of the fossil Echini peculiar to Switzerland. In the same year appeared the first number of a more extensive work, having the title of "Monographies d'Echinodermes." This number contained the monograph of the Salenia, small Echini belonging to the chalk. was followed by three others, treating of the Scutellæ, the Galerites, and the anatomy of the Echinus,-the last number edited by M. Valentin. To facilitate the study of these curious animals, so important to the history of successive creations, Agassiz made casts in plaster of all the specimens in his possession. This collection comprises casts of nearly five


* A formation_belonging to the lower green-sand, near Neufchatel, from the Latin name of which city it derives its name.

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