of evolution. These facts, however, do not necessarily prove more than that some species possess a greater variability than others, and (what is indeed unquestionable) that species have often been unduly multiplied by geologists and botanists. It may be, for example, that Wagner was right, and that all the American monkeys of the genus cebus may be reduced to a single species, or to two.

With regard to the lower organisms, and supposing views recently advanced to become fully established, there is no reason to think that the forms said to be evolved were new species, but rather reappearances of definite kinds which had appeared before and will appear again under the same conditions. So with higher forms, similar conditions must educe similar results; but here practically similar conditions can rarely obtain, because of the large part which "descent" and "inheritance" always play in such highly organized forms.

Still it is conceivable that different combinations at different times may have occasionally the same outcome, just as the multiplications of different numbers may have severally the same result.

There are reasons, however, for thinking it possible that the human race is a witness of an exceptionally unchanging and stable condition of things, if the calculations of Mr. Croll are valid as to how far variations in the eccentricity in the earth's orbit, together with the precession of the equinoxes, have produced changes in climate. Mr. Wallace has pointed out1 that, as during the last 60,000 years

1 See Nature, March 3, 1870, p. 454. Mr. Wallace says (referring to Mr. Croll's paper in the Phil. Mag.), “As we are now, and have been for 60,000 years, in a period of low eccentricity, the rate of change of species during that time may be no measure of the rate that has generally obtained in past geological epochs."

these conditions have been exceptionally unchanging, specific evolution may have been exceptionally rare. It becomes then possible to suppose that for a similar period stimuli to change in the manifestation of animal forms may have been unusually few and feeble, that is, if the conditions of the earth's orbit have been as exceptional as stated. However, even if new species are now being evolved as actively as ever, or if they have been so quite recently, no conflict thence necessarily arises with the view here advocated. For it by no means follows that if some examples of new species have recently been suddenly produced from individuals of antecedent species, we ought to be able to put our fingers on such cases; as Mr. Murphy well observes 1 in a passage before quoted, "If a species were to come suddenly into being in a wild state, as the Ancon sheep did under domestication, how could we ascertain the fact? If the first of a newly-born species were found, the fact of its discovery would tell nothing about its origin. Naturalists would register it as a very rare species, having been only once met with, but they would have no means of knowing whether it were the first or the last of its race."

But are there any grounds for thinking that in the genesis of species an internal force or tendency intervenes, co-operating with and controlling the action of external conditions?

It is here contended that there are such grounds, and that though inheritance, reversion, atavism, Natural Selection, &c., play a part not unimportant, yet that such an internal power is a great, perhaps the main, determining agent.

1 "Habit and Intelligence," vol. i. p. 344.

It will, however, be replied that such an entity is no vera causa; that if the conception is accepted, it is no real explanation; and that it is merely a roundabout way of saying that the facts are as they are, while the cause remains unknown. To this it may be rejoined, that for all who believe in the existence of the abstraction "force" at all, other than will, this conception of an internal force must be accepted and located somewhere-cannot be eliminated altogether; and that therefore it may as reasonably be accepted in this mode as in any other.

It was urged at the end of the third chapter, that it is congruous to credit mineral species with an internal power or force. By such a power it may be conceived that crystals not only assume their external symmetry, but even repair it when injured. Ultimate chemical elements must also be conceived as possessing an innate tendency to form certain unions, and to cohere in definite aggregations. This was considered towards the end of Chapter VIII.

Turning to the organic world, even on the hypothesis of Mr. Herbert Spencer or that of Mr. Darwin, it is impossible to escape the conception of innate internal forces. With regard to the physiological units of the former, Mr. Spencer himself, as we have seen, distinctly attributes to them "an innate tendency" to evolve the parent form from which they sprang. With regard to the gemmules of Mr. Darwin, we have seen in Chapter X. with how many innate powers, tendencies, and capabilities they must each be severally endowed to reproduce their kind, to evolve complex organisms or cells, to exercise germinative affinity, &c.

If then (as was before said at the end of Chapter VIII.) such innate powers must be attributed to chemical atoms,

to mineral species, to gemmules, and to physiological units, it is only reasonable to attribute such to each individual organism.

The conception of such internal and latent capabilities. is somewhat like that of Mr. Galton, before mentioned, according to which the organic world consists of entities, each of which is, as it were, a spheroid with many facets on its surface, upon one of which it reposes in stable equilibrium. When by the accumulated action of incident forces this equilibrium is disturbed, the spheroid is supposed to turn over until it settles on an adjacent facet once more in stable equilibrium.

The internal tendency of an organism to certain considerable and definite changes would correspond to the facets on the surface of the spheroid.

It may be objected that we have no knowledge as to how terrestrial, cosmical, and other forces can affect organisms so as to stimulate and evolve these latent, merely potential forms. But we have had evidence that such mysterious agencies do affect organisms in ways as yet inexplicable, in the very remarkable effects of geographical conditions which were detailed in the third chapter.

It is quite conceivable that the material organic world may be so constituted that the simultaneous action upon it of all known forces, mechanical, physical, chemical, magnetic, terrestrial, and cosmical, together with other as yet unknown forces which probably exist, may result in changes which are harmonious and symmetrical; just as the internal nature of vibrating plates causes particles of sand scattered over them to assume definite and symmetrical figures when made to oscillate in different ways by

the bow of a violin being drawn along their edges.1 The results of these combined internal powers and external influences might be represented under the symbol of complex series of vibrations (analogous to those of sound or light) forming a most complex harmony or a display of most varied colours. In such a way the reparation of local injuries might be symbolized as a filling up and completion of an interrupted rhythm. Thus also monstrous aberrations from typical structure might correspond to a discord, and sterility from crossing be compared with the darkness resulting from the interference of waves of light.

Such symbolism will harmonize with the peculiar reproduction, before mentioned, of heads in the body of certain annelids, with the facts of serial homology, as well as

1 In his recently published work on Man, Mr. Darwin has made some very remarkable admissions as to the existence of an internal force such as is here contended for. Thus, in vol. ii. p. 388, speaking of certain modifications, he says: "In the greater number of cases we can only say that the cause of each slight variation, and of each monstrosity, lies much more in the nature and constitution of the organism than in the nature of the surrounding conditions." Again, speaking of the disappearance of spots and stripes in pigs, deer, and tapirs, he remarks: "Whether this change was effected through sexual or natural selection, or was due to the direct action of the conditions of life, or some other unknown cause, it is impossible to decide" (Op. cit. p. 305). In the first volume, p. 154, he says of the exciting causes of modifications: They relate much more closely to the constitution of the varying organism than to the nature of the conditions to which it has been subjected." He also speaks (p. 225) of "unknown differences in the constitution" as the undoubted cause of certain degrees of sterility. Finally, with regard to the transformation of specific characters we have the following noteworthy passage: "An unexplained residuum of change, perhaps a large one, must be left to the assumed uniform action of those unknown agencies, which occasionally induce strongly-marked and abrupt deviations of structure in our domestic productions."-("Descent of Man," vol. i. p. 154.) In this passage Mr. Darwin seems to admit all that the author of this book need demand.

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