This well-rounded cla.s.sification of animal forms is in a sense the crown of Cuvier's work, for the principle of the subordination of characters, in the interpretation which he gives to it, is a direct application of his principle of functional correlation. Each of the great groups is built upon one plan. The idea of the unity of plan has become for Cuvier a commonplace of his thought, and it is tacitly recognised in all his anatomical work. But he never takes it as a hard-and-fast principle which must at all costs be imposed upon the facts.

Cuvier has become known as the greatest champion of the fixity of species, but it is not often recognised that his att.i.tude to this problem is at least as scientific as that of the evolutionists of his own and later times. No doubt he became dogmatic in his rejection of evolution-theory, but he was on sure ground in maintaining that the evolutionists of his day went beyond their facts. He considered that certain forms (species) have reproduced themselves from the origin of things without exceeding the limits of variation. His definition of a species was, "the individuals descended from one another or from common parents, together with those that resemble them as much as they resemble one another."[62] "These forms are neither produced nor do they change of themselves; life presupposes their existence, for it cannot arise save in organisations ready prepared for it."[63]

He based his rejection of all theories of descent upon the absence of definite evidence for evolution. If species have gradually changed, he argued, one ought to find traces of these gradual modifications.[64]

Palaeontology does not furnish such traces. Again, the limits of variation, even under domestication, are narrow, and the most extreme variation does not fundamentally alter the specific type. Thus the dog has varied perhaps most of all, in size, in shape, in colour. "But throughout all these variations the relations of the bones remain the same, and the form of the teeth never changes to an appreciable extent; at most there are some individuals in which an additional false molar develops on one side or the other."[65] This second objection is the objection of the morphologist. It would be an interesting study to compare Cuvier's views on variation with those of Darwin, who was essentially a systematist.

Cuvier's first objection was of course determined to some extent by the imperfection of the palaeontological knowledge of his time. But even at the present day the objection has a certain force, for although we have definite evidence of many serial transformations of one species into another along a single line, for example, Neumayr's _Paludina_ series, yet at any one geological level the species, the lines of descent, are all distinct from one another.[66]

Cuvier recognised very clearly that there is a succession of forms in time, and that on the whole the most primitive forms are the earliest to appear. Mammals are later than reptiles, and fishes appear earlier than either. As Deperet puts it, "Cuvier not only demonstrated the presence in the sedimentary strata of a series of terrestrial faunas superimposed and distinct, but he was the first to express, and that very clearly, the idea of the gradual increase in complexity of these faunas from the oldest to the most recent" (p. 10).

He did not believe that the fauna of one epoch was transformed into the fauna of the next. He explained the disappearance of the one by the hypothesis of sudden catastrophes, and the appearance of the next by the hypothesis of immigration. He nowhere advanced the hypothesis of successive new creations. "For the rest, when I maintain that the stony layers contain the bones of several genera and the earthy layers those of several species which no longer exist, I do not mean that a new creation has been necessary to produce the existing species, I merely say that they did not exist in the same localities and must have come thither from elsewhere."[67] It was left to d'Orbigny to teach the doctrine of successive creations, of which he distinguished twenty-seven (_Cours elementaire de palaeontologie stratigraphique_, 1849).

Cuvier, however, can hardly have believed that all species were present at the beginning, since he does admit a progression of forms.

Probably he had no theory on the subject, for theories without facts had little interest for him. At any rate it is a mistake to think that Cuvier was a supporter of the theological doctrine of special creation. His philosophy of Nature was mechanistic, and he dedicated his _Recherches sur les Oss.e.m.e.ns Fossiles_ to his friend Laplace. He admitted the idea of evolution at least so far as to conceive of a development of man from a savage to a civilised state.[68] He refused to accept the extravagant evolutionary theory of Demaillet and the somewhat confused theory of Lamarck (whom he joins with Demaillet),[69]

just as he rejected the transcendental theories of Geoffroy St Hilaire, because they seemed to him not based upon facts.

[41] _Lecons d'Anatomie Comparee_, tome i., pp. 10 _et scq._, 1800.

[42] _Lecons d'Anatomie Comparee_, i., p. 18.

[43] _Loc. cit._, i., p. 13.

[44] _Lecons d'Anatomie Comparee_, tome i., Articles iii.-iv., 1800.

[45] _Lecons d'Anatomie Comparee_, i., p. 47.

[46] _Le Regne Animal_, i., p. 6, 1817.

[47] _Histoire des Progres des Sciences naturelles depuis 1789_, i., p. 310, 1826.

[48] _Recherches sur les Oss.e.m.e.ns Fossiles_, i., p. 60, 1812.

[49] _Oss.e.m.e.ns fossiles_, i., p. 60.

[50] _Loc. cit._, i., p. 63.

[51] _Lecons d'Anatomie Comparee_, i., p. 6.

[52] _Le Regne Animal_, i., p. 16.

[53] _Hist. Prog. Sci. Nat._, i., p. 187, 1826.

[54] _Lecons_, i., p. 58.

[55] _Loc. cit._, i., Article iii.

[56] _Loc. cit._, i., p. 60.

[57] _Regne Animal_, i., p. xx.

[58] Cuvier, _Hist. Prog. Sci. Nat._, i., p. 288, 1826.

[59] _Regne Animal_, i., p. 10.

[60] _Regne Animal_, p. 55.

[61] First propounded by Cuvier in 1812, _Ann. Mus.

d'Hist. Nat._, xix.

[62] _Regne Animal_, i., p. 19.

[63] _Loc. cit._, p. 20.

[64] _Recherches sur les Oss.e.m.e.ns Fossiles_, i., p. 74, 1812.

[65] _Loc. cit._, p. 79.

[66] See C. Deperet, _Les transformations du Monde animal_, Paris, 1907, and G. Steinmann, _Die geologischen Grundlagen der Abstammungslehre_, Leipzig, 1908.

[67] _Recherches_, i., p. 81.

[68] _Regne Animal_, i., p. 91.

[69] _Oss.e.m.e.ns Fossiles_, i., p. 26.

CHAPTER IV

GOETHE

Science, in so far as it rises above the mere acc.u.mulation of facts, is a product of the mind's creative activity. Scientific theories are not so much formulae extracted from experience as intuitions imposed upon experience. So it was that Goethe, who was little more than a dilettante,[70] seized upon the essential principles of a morphology some years before that morphology was accepted by the workers.

Goethe is important in the history of morphological method because he was the first to bring to clear consciousness and to express in definite terms the idea on which comparative anatomy before him was based, the idea of the unity of plan. We have seen that this idea was familiar to Aristotle and that it was recognised implicitly by all who after him studied structure comparatively. In Goethe's time the idea had become ripe for expression. It was used as a guiding principle in Goethe's youth particularly by Vicq d'Azyr and by Camper. The former (1748-1794), who discovered[71] in the same year as Goethe (1784) the intermaxillary bone in man, pointed out the h.o.m.ology in structure between the fore limb and the hind limb, and interpreted certain rudimentary bones, the intermaxillaries and rudimentary clavicles, in the light of the theory that Vertebrates are built upon one single plan of structure.

"Nature seems to operate always according to an original and general plan, from which she departs with regret and whose traces we come across everywhere" (Vicq d'Azyr, quoted by Flourens, _Mem. Acad.

Sei._, XXIII., p. x.x.xvi.).

Peter Camper (1722-1789), we are told by Goethe himself in his _Osteologie_, was convinced of the unity of plan holding throughout Vertebrates; he compared in particular the brain of fishes with the brain of man.

The idea of the unity of plan had not yet become limited and defined as a strictly scientific theory; it was an idea common to philosophy, to ordinary thought, and to anatomical science. We find it expressed by Herder (who perhaps got it from Kant) in his _Ideen sur Philosophie der Geschichte der Menschheit_ (1784), and it is possible that Goethe became impressed with the importance of the idea through his conversations with Herder. Be that as it may, it is certain that Goethe sought for the intermaxillaries in man only because he was firmly convinced that the skeleton in all the higher animals was built upon one common plan and that accordingly bones such as the intermaxillaries, found well developed in some animals, must also be found in man. The idea was not drawn from the facts, but the facts were interpreted and even sought for in the light of the idea. "I eagerly worked upon a general osteological scheme, and had accordingly to a.s.sume that all the separate parts of the structure, in detail as in the whole, must be discoverable in all animals, because on this supposition is built the already long begun science of comparative anatomy."[72]

The principle comes to clear expression in his _Erster Entwurf einer allgemeinen Einleitung in die vergleichende Anatomie_ (1795).[73] He writes:--"On this account an attempt is here made to arrive at an anatomical type, a general picture in which the forms of all animals are contained in potentia, and by means of which we can describe each animal in an invariable order."[74] His aim is to discover a general scheme of the constant in organic parts, a scheme into which all animals will fit equally well, and no animal better than the rest.

When we remember that the type to which anatomists before him had, consciously or unconsciously, referred all other structure was man himself, we see that in seeking after an abstract generalised type Goethe was reaching out to a new conception. The fact that only the structure of man and the higher animals was at all well-known in his time led Goethe to think that his general Typus would hold for the lower animals as well, though it was to be arrived at primarily from a study of the higher animals. All he could a.s.sert of the entire animal kingdom was that all animals agreed in having a head, a middle part, and an end part, with their characteristic organs, and that accordingly they might, in this respect at least, be reduced to one common Typus. Goethe's knowledge of the lower animals was not extensive.

Though Goethe did not work out a criterion of the h.o.m.ology of parts with any great clearness, he had an inkling of the principle later developed by E. Geoffroy St Hilaire, and called by him the "Principle of Connections." According to this principle, the h.o.m.ology of a part is determined by its position relative to other parts. Goethe expresses it thus:--"On the other hand the most constant factor is the position in which the bone is invariably found, and the function to which it is adapted in the organic edifice."[75] But from this sentence it is not clear that Goethe understood the principle as one of form independent of function, for he seems to consider that the h.o.m.ology of an organ is partly determined by the function which it performs for the whole. He wavers between the purely formal or morphological interpretation of the principle of connections and the functional. We find him in the additions to the _Entwurf_ (1796), saying:--"We must take into consideration not merely the spatial relations of the parts, but also their living reciprocal influence, their dependence upon and action on one another." [76] But in seeking for the intermaxillary bone in man he was guided by its position relative to the maxillaries--it must be the bone between the anterior ends of the maxillaries, a bone whose limits are indicated in the adult only by surface grooves.