We have given prominence, in the first instance, to the doctrine of "spontaneous" or "aboriginal" production, because it constitutes an indispensable part of the Theory of Development, and because we believe that, were this clearly understood, that theory would soon sink into general discredit or total oblivion, like the kindred speculations of Anaximander and Anaxagoras, of the old Ionic School. The experiments of Ehrenberg, instituted with the view of testing the doctrine of spontaneous generation, may be said to have decided the whole question. They did not succeed, indeed, in explaining every apparently exceptional case, for some of the facts are still obscure, and will probably continue to be so, notwithstanding every extension of microscopic power, just as, in the analogous case of the Nebulae, the increase of telescopic power has enabled us to resolve not a few of them into clusters of stars, while it has served to bring others yet unresolved within the range of our vision. But they were sufficient, at least, to show that, as far as our clear knowledge extends, the one uniform law, "_Omne vivum ex ovo_," universally prevails, and that the whole analogy of Nature, in so far as its constitution has been ascertained, is adverse to the doctrine of spontaneous generation. 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.