dification of the form, colour, size, structure, or other particulars; but the mutations thus superinduced are governed by constant laws, and the capability of so varying forms part of the specific character.

'3. Some acquired peculiarities of form, structure, and instinct are transmissible to the offspring; but these consist of such qualities and attributes only as are intimately related to the natural wants and propensities of the species.

'4. The entire variation from the original type, which any given kind of change can produce, may usually be effected in a brief period of time, after which no farther deviation can be attained by continuing to alter the circumstances, though ever so gradually; indefinite divergence, either in the way of improvement or deterioration, being prevented, and the least possible excess beyond the definite limits being fatal to the existence of the individual.

'5. The intermixture of the distinct species is guarded against by the aversion of the individuals composing them to sexual union, or by the sterility of the mule offspring. It does not appear that true hybrid races have ever been perpetuated for several generations, even by the assistance of man; for the cases usually cited relate to the crossing of mules with individuals of pure species, and not to the intermixture of hybrid with hybrid.

'6. From the above considerations, it appears that species have a real existence in nature; and that each was endowed, at the time of its creation, with the attributes and organization by which it is now distinguished1.

STRATA IDENTIFIED BY ORGANIC REMAINS.

The discovery by William Smith of the successive stages of the stratification of Britain, each containing the remains of the organic beings then living in the waters or distributed through their agency, each stratum having been in succession the bed of the sea, gave the basis of a true Palæontology, and a true history of the succession of life on the globe. Almost every geologist and naturalist who has read this history by the light of these discoveries has arrived at the conclusion that many separate acts of creation are required to explain the successive appearances of the various races of animals and plants. In a few instances, of late years, the attempt has been made to adapt the hypothesis of Lamarck to the facts of Geology, and to combine two really distinct ideas-to derive all the observed variety of organization from one or a few original germs, by steps continually ascending on the whole to higher

1 Principles of Geology, Book III. conclusion of Chap. Iv.

grades and greater perfection as a physiological problem; and to shew that in the buried worlds of life this continual expansion of the general fundamental form, with a continual tendency to higher and higher development, can be placed in evidence as a matter of history. It is important to keep this distinction in mind.

DEVELOPMENT.

The author of the Vestiges of Creation placed before the English reader some sketches of the aspect of the animated world in successive geological ages, and has proposed in relation to the vegetable and animal kingdoms a full hypothesis of development to fit the gradation from the simple Lichen and Animalcule respectively up to the highest order of Dicotyledonous trees and the Mammalia. He attributes a great amount of change to the necessary effect of variations in the physical conditions which are influential on life: this change being progressive from lower to higher grades, and unlimited except by the range of physical conditions.

'While the external forms of the various vertebrate animals are so different, the whole are, after all, variations of a fundamental plan, which can be traced as a basis through the whole, the variations being merely modifications of that plan to suit the particular conditions in which each particular animal has been designed to live. Starting from the primeval germ, which is the representative of a particular order of full-grown animals, we find all others to be merely advances from that type, with the extension of endowments and modification of forms which are required in each particular case: each form, also, retaining a strong affinity to that which precedes it, and tending to impress its own features on that which succeeds.

'The various organic forms of our world are bound up in one-a fundamental unity pervades and embraces them all, collecting them, from the humblest lichen up to the highest mammifer, in one system, the whole creation of which must have depended upon one law or decree of the Almighty, though it did not all come forth at one time. The idea of a separate creation for each must appear totally inadmissible. The single fact of abortive or rudimentary organs condemns it; for these, on such a supposition, could be regarded in no other light than as blemishes or blunders, the thing of all others most irreconcileable with that idea of Almighty Perfection which a general view of nature so irresistibly conveys. On the other hand, when the organic creation is admitted to have been effected by a general law, we see nothing in these abortive parts but harmless

peculiarities of development, and interesting evidences of the manner in which the Divine Author has been pleased to work.

'The whole train of animated beings, from the simplest and oldest up to the highest and most recent, are thus to be regarded as a series of advances of the principle of development, which have depended upon external physical circumstances to which the resulting animals are appropriate. I contemplate the whole phenomena,' he says, 'as having been in the first place arranged in the councils of the Divine Wisdom, to take place, not only upon this sphere, but upon all the others in space, under necessary modifications, and as being carried on, from first to last, here and elsewhere, under immediate favour of the creative will or energy. We are drawn to the supposition that the first step in the creation of life upon this planet was a chemicoelectric operation, by which simple germinal vesicles were produced.' After this it is suggested, 'as an hypothesis already countenanced by much that is ascertained, and likely to be further sanctioned by much that remains to be known, that the first step was an advance under favour of peculiar conditions, from the simplest forms of being, to the next more complicated, and this through the medium of the ordinary process of generation.'