It is clear, from what has just been said, that the many angry discussions respecting the fixity of species, which, since the days of Lamarck, have disturbed the amity of zoologists and speculative philosophers, would have been considerably abbreviated, had men distinctly appreciated the equivoque which rendered their arguments hazy. I am far from implying that the battle was purely a verbal one. I believe there was a real and important distinction in the doctrines of the two camps; but it seems to me that had a clear understanding of the fact that Species was an abstract term, been uniformly present to their minds, they would have sooner come to an agreement. Instead of the confusing disputes as to whether one Species could ever become another Species, the question would have been, Are animal forms changeable? Can the descendants of animals become so _unlike their ancestors_, in certain peculiarities of structure or instinct, as to be classed by naturalists as a different species? No sooner is the question thus disengaged from equivoque, than its discussion becomes narrowed within well-marked limits. That animal forms _are_ variable, is disputed by no zoologist. The only question which remains is this: _To what extent_ are animal forms variable? The answers given have been two: one school declaring that the extent of variability is limited to those trifling characteristics which mark the different Varieties of each Species; the other school declaring that the variability is indefinite, and that all animal forms may have arisen from successive modifications of a very few types, or even of one type. Now, I would call your attention to one point in this discussion, which ought to be remembered when antagonists are growing angry and bitter over the subject: it is, that both these opinions are necessarily hypothetical—there can be nothing like positive proof adduced on either side. The utmost that either hypothesis can claim is, that it is more consistent with general analogies, and better serves to bring our knowledge of various points into harmony. Neither of them can claim to be a truth which warrants dogmatic decision.