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 are variable, they have meant that animal forms are variable; and these variations, gradually accumulating, result at last in such differences as are called specific. Although some zoologists, and speculators who were not zoologists, have believed that the possibility of variation is so great that one species may actually be transmuted into another, i.e., that an ass may be developed into a horse,—yet most thinkers are now agreed that such violent changes are impossible; and that every new form becomes established only through the long and gradual accumulation of minute differences in divergent directions.

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.

Of these two hypotheses, the first has the weight and majority of authoritative adherents. It declares that all the different kinds of Cats, for example, were distinct and independent creations, each species being originally what we see it to be now, and what it will continue to be as long as it exists: lions, panthers, pumas, leopards, tigers, jaguars, ocelots, and domestic cats, being so many original stocks, and not so many divergent forms of one original