Critiques and Addresses

by Thomas Henry Huxley

On this hypothesis, hereditary transmission is the result of the victory of particular molecules contained in the impregnated germ. Adaptation to conditions is the result of the favouring of the multiplication of those molecules whose organizing tendencies are most in harmony with such conditions. In this view of the matter, conditions are not actively productive, but are passively permissive; they do not cause variation in any given direction, but they permit and favour a tendency in that direction which already exists.

It is true that, in the long run, the origin of the organic molecules themselves, and of their tendencies, is to be sought in the external world; but if we carry our inquiries as far back as this, the distinction between internal and external impulses vanishes. On the other hand, if we confine ourselves to the consideration of a single organism, I think it must be admitted that the existence of an internal metamorphic tendency must be as distinctly recognized as that of an internal conservative tendency; and that the influence of conditions is mainly, if not wholly, the result of the extent to which they favour the one, or the other, of these tendencies.

III. There is only one point upon which I fundamentally and entirely disagree with Professor Haeckel, but that is the very important one of his conception of geological time, and of the meaning of the stratified rocks as records and indications of that time. Conceiving that the stratified rocks of an epoch indicate a period of depression, and that the intervals between the epochs correspond with periods of elevation of which we have no record, he intercalates between the different epochs, or periods, intervals which he terms "Ante-periods." Thus, instead of considering the Triassic, Jurassic, Cretaceous, and Eocene periods, as continuously successive, he interposes a period before each, as an "Antetrias-zeit," "Antejura-zeit," "Antecreta-zeit," "Antecocen-zeit," &c. And he conceives that the abrupt changes between the Faunae of the different formations are due to the lapse of time, of which we have no organic record, during their "Ante-periods."

The frequent occurrence of strata containing assemblages of organic forms which are intermediate between those of adjacent formations, is, to my mind, fatal to this view. In the well-known St. Cassian beds, for example, Palaeozoic and Mesozoic forms are commingled, and, between the Cretaceous and the Eocene formations, there are similar transitional beds. On the other hand, in the middle of the Silurian series, extensive unconformity of the strata indicates the lapse of vast intervals of time between the deposit of successive beds, without any corresponding change in the Fauna.

Professor Haeckel will, I fear, think me unreasonable, if I say that he seems to be still overshadowed by geological superstitions; and that he will have to believe in the completeness of the geological record far less than he does at present. He assumes, for example, that there was no dry land, nor any terrestrial life, before the end of the Silurian epoch, simply because, up to the present time, no indications of fresh water, or terrestrial organisms, have been found in rocks of older date. And, in speculating upon the origin of a given group, he rarely goes further back than the "Ante-period," which precedes that in which the remains of animals belonging to that group are found. Thus, as fossil remains of the majority of the groups of Reptilia are first found in the Trias, they are assumed to have originated in the "Antetriassic" period, or between the Permian and Triassic epochs.

I confess this is wholly incredible to me. The Permian and the Triassic deposits pass completely into one another; there is no sort of discontinuity answering to an unrecorded "Antetrias;" and, what is more, we have evidence of immensely extensive dry land during the formation of these deposits. We know that the dry land of the Trias absolutely teemed with reptiles of all groups except Pterodactyles, Snakes, and perhaps Tortoises; there is every probability that true Birds existed, and Mammalia certainly did. Of the inhabitants of the Permian dry land, on the contrary, all that have left a record are a few lizards. Is it conceivable that these last should really represent the whole terrestrial population of that time, and that the development of Mammals, of Birds, and of the highest forms of Reptiles, should have been crowded into the time during which the Permian conditions quietly passed away, and the Triassic conditions began? Does not any such supposition become in the highest degree improbable, when, in the terrestrial or fresh-water Labyrinthodonts, which lived on the land of the Carboniferous epoch, as well as on that of the Trias, we have evidence that one form, of terrestrial life persisted, throughout all these ages, with no important modification? For my part, having regard to the small amount of modification (except in the way of extinction) which the Crocodilian, Lacertilian, and Chelonian Reptilia have undergone, from the older Mesozoic times to the present day, I cannot but put the existence of the common stock from which they sprang far back in the Palaeozoic epoch; and I should apply a similar argumentation to all other groups of animals.

IV. Professor Haeckel proposes a number of modifications in Taxonomy, all of which are well worthy of consideration. Thus he establishes a third primary division of the living world, distinct from both animals and plants, under the name of the Protista, to include the Myxomycetes, the Diatomaceae, and the Labyrinthulae, which are commonly regarded as plants, with the Noctilucae, the Flagellata, the Rhizopoda, the Protoplasta, and the Monera, which are most generally included within the animal world. A like attempt has been made, by other writers, to escape the inconvenience of calling these dubious organisms by the name of plant or animal; but I confess, it appears to me, that the inconvenience which is eluded in one direction, by this step, is met in two others. Professor Haeckel himself doubts whether the Fungi ought not to be removed into his Protista. If they are not, indeed, the Myxomycetes render the drawing of every line of demarcation between Protista and Plants impossible. But if they are, who is to define the Fungi from the Algae? Yet the sea-weeds are surely, in every respect, plants. On the other hand, Professor Haeckel puts the sponges among the Coelenterata (or polypes and corals), with the double inconvenience, as it appears to me, of separating the sponges from their immediate kindred, the Protoplasta, and destroying the definition of the Coelenterata. So again, the Infusoria possess all the characters of animality, but it can hardly be said that they are as clearly allied to the worms as they are to the Noctilucae.

On the whole, it appears to me to be most convenient to adhere to the old plan of calling such of these low forms as are more animal in habit, Protozoa, and such as are more vegetal, Protophyta.

Another considerable innovation is the proposition to divide the class Pisces into the four groups of Leptocardia, Cyclostomata, Pisces, and Dipneusta. As regards the establishment of a separate class for the Lancelet (Amphioxus), I think there can be little doubt of the propriety of so doing, inasmuch as it is far more different from all other fishes than they are from one another. And there is much to be said in favour of the same promotion of the Cyclostomata, or Lampreys and Hags. But considering the close relation of the Mudfish with the Ganoidei, and the wide differences between the Elasmobranchii and the Teleostei, I greatly doubt the propriety of separating the Dipneusta, as a class, from the other Pisces.

Professor Haeckel proposes to break up the vertebrate sub-kingdom, first, into the two provinces of Leptocardia and Pachycardia; Amphioxus being in the former, and all other vertebrates in the latter division. The Pachycardia are then divided into Monorhina, which contains the Cyclostome fishes, distinguished by their single nasal aperture; and Amphirhina, comprising the other Vertebrata, which have two nasal apertures. These are further subdivided into Anamnia (Pisces, Dipneusta, Amphibia) and Amniota (Reptilia, Aves, Mammalia). This classification undoubtedly expresses many of the most important facts in vertebrate structure in a clear and compendious way; whether it is the best that can he adopted remains to be seen.