Each of these assumptions is necessarily involved in any attempt to account for the origin of the vegetable and animal races by natural law, without direct Divine interposition.

For if, after the first organism was brought into being, the production of every subsequent type may be accounted for simply by a transmutation of species, yet the production of the original organism itself, or the first commencement of life in any form, must necessarily be ascribed either to a creative act or to spontaneous generation.

A new product is supposed to have come into being, differing from any that ever existed before it, in the possession of vital and reproductive powers; and this product can only be ascribed, if Creation be denied, to the spontaneous action of some element, such as Electricity, on mucus or albumen.

In this sense the doctrine of spontaneous generation seems to be necessarily involved in the first step of the process of Development, and is, indeed, indispensable, if any account is to be given of the origin of vegetable and animal life; but in the subsequent steps of the same process it is superseded by a supposed transmutation of species, whereby a lower form of life is said to rise into a higher, and an inferior passes into a more perfect organism.
But we have no experience either of spontaneous generation on the one hand, or of a transmutation of species on the other.

Observation has not discovered, nor has history recorded, an authentic example of either.