The reason of his anxiety to avail himself of these cases is evident.

The exigencies of his theory demanded a method of accounting for the primary origin of life different from any that can be found in the common process of propagation.

He saw clearly enough that his main argument, founded, as it was, on the law of hereditary transmission, could not account for the production of the first organism; and that, if he would avoid either the doctrine of _Immediate Creation_, which is so offensive to him, or the idea of _Eternal Generation_, which is utterly excluded by the clearest lessons of Fossil Geology, he must have recourse to the hypothesis of _Spontaneous Generation_.

Hence he attempts to account for the commencement of new species both of plants and animals, in the course of the world's history, by a transmutation of species; while, for the origin of the first species, he has recourse to the same law of Development, but acting in widely different circumstances, and giving rise to what he calls "aboriginal generation," whereby the inorganic passes into the organic, and life, form, and structure, are imparted to hitherto inert materials by the action of Electricity on mucus or albumen.

To accomplish this twofold purpose, he felt it necessary to insist, in the first instance, on the ordinary law of generation as the established order of _mediate_ creation; while he found it equally necessary, in the second place, to insist on those apparently exceptional cases in which the connection between the germ and the product has hitherto eluded philosophical research,--and this for the purpose of showing that the original production of plants and animals was _not similar_ to the ordinary method of their propagation in any other respect than this, that in both cases the result is brought about by Natural Laws, without the direct interposition of any supernatural cause.
Now, in so far as his argument is founded on the principle of analogy,--and it is on this principle that it proceeds throughout,--we submit that it is radically vicious, and utterly inconclusive.