Ehrenberg detected the minute germs of vegetable mould, and the ova of some of the smallest animalcules; and when it is considered that these germs and ova are so tenacious of vitality that certain prolific seeds have come down to us from the age of the Pharaohs in the wrappings of the Egyptian mummies,--that they are widely diffused in the air and the waters, insomuch that no sooner does a coral reef appear above the level of the sea than it is forthwith covered with herbage by means of seeds wafted by the winds or deposited by the waves,--and that it is almost impossible to exclude them by any artificial expedient, since they are capable of resisting the action of boiling water and even of alcohol itself,--it cannot, we think, be denied that the few cases which still remain obscure or unexplained may be, at least, _probably_ accounted for in accordance with the same natural law which is found to be invariably established in every department to which our clear knowledge extends.
In regard, again, to the supposed "transmutation of species," we are equally warranted in affirming that it is destitute of all experimental evidence, and unsupported even by any natural analogy.

As the doctrine of spontaneous generation stands opposed to the maxim that _organic life can be produced only by organic life_, so the doctrine of a transmutation of species stands opposed to the equally certain maxim that _like produces like, both in the vegetable and animal kingdoms_.
Cuvier has demonstrated, with reference to the birds and reptiles preserved in Egypt, an entire fixity and uniformity of species, in every, even the least, particular, for at least three thousand years.[48] In the actual course of Nature we see no tendency to change; nay, a barrier seems to have been erected in the constitution of Nature itself to prevent the possible confusion of races by promiscuous intercourse, through that provision which renders the mule incapable of reproduction.

No plant has ever been found in a state of transition from a lower to a higher form; no instance has ever been produced of one of the algae being transmuted into the lowest form of terrestrial vegetation; nor of a small gelatinous body developing itself into a fish, a bird, or a beast; nor of an ourang-outang rising into a man.[49] It is true, indeed, that "there is a capacity in all species to accommodate themselves, to a certain extent, to a change of external circumstances, this extent varying greatly according to the species.
There may thus arise changes of appearance or structure, and some of these changes are transmissible to the offspring; but the mutations thus superinduced are _governed by constant laws and confined within certain limits_.

Indefinite divergence from the original type is not possible, and the extreme limit of possible variation may usually be reached in a short period of time; in short, species have a real existence in Nature, and a transformation from one to another does not exist."[50] The whole science of Natural History is based on the existence of distinct species, capable of being discriminated from each other by certain characteristic marks; and the whole art of the agriculturist and the stockbreeder proceeds on the assumption of a law, invariable in its operation, whereby "like produces like in the vegetable and animal worlds." The instances to which the author of "The Vestiges" refers in support of his theory are utterly frivolous when opposed to the copious inductions to which they are opposed; and they may all be explained consistently with the _law of variation within definite limits_, as stated by Dr.Whewell, or by our ignorance of all the conditions involved in each particular case.

Nor is his argument founded on the limited range of our observation, even with its singular illustration derived from Mr.Babbage's calculating engine, fitted to diminish, in the slightest degree, our confidence in the general results of these inductions; for, not to mention that it amounts to nothing more than an appeal from what we do know to what we do not know, from knowledge to ignorance, from the certainties of science to the mere possibilities of conjecture, it has been well shown by Mr.Miller, that our range of observation is not so limited as the author of "The Vestiges" would have us to believe, since "_extent of space_ is, in a matter of this kind, equivalent to _duration of time_.