“In considering these questions we should remember how slight are most of those specific differences, the origin of which gives rise to so much controversy, in comparison with the cycle of changes undergone by every individual in the course of its development. There are numerous genera, including many very closely allied species, distinguished by differences which, were it not for the fact that they have remained unchanged and invariable through ages, might be termed insignificant. Such, for instance, are the various species of corals found in the everglades of Florida, where they lived and died ages ago, and had the identical specific differences by which we distinguish their successors in the present Florida reefs. The whole science of zoölogy in its present condition is based upon the fact that these slight differences are maintained generation after generation. And yet every individual on such a coral stock,—and the same is true of any individual in any class whatsoever of the whole animal kingdom, whether Radiate, Mollusk, Articulate, or Vertebrate,—before reaching its adult condition and assuming the permanent characters which distinguish it from other species, and have never been known to vary, passes in a comparatively short period through an extraordinary transformation, the successive phases of which differ far more from each other than do the adult species. In other words, the same individual differs more from himself in successive stages of his growth than he does in his adult condition from kindred species of the same genus. The conclusion seems inevitable, that, if the slight differences which distinguish species were not inherent, and if the phases through which every individual has to pass were not the appointed means to reach that end, themselves invariable, there would be ever-recurring deviations from the normal types. Every naturalist knows that this is not the case. All the deviations known to us are monstrosities, and the occurrence of these, under disturbing influences, are to my mind only additional evidence of the fixity of species. The extreme deviations obtained in domesticity are secured, as is well known, at the expense of the typical characters, and end usually in the production of sterile individuals. All such facts seem to show that so-called varieties or breeds, far from indicating the beginning of new types, or the initiating of incipient species, only point out the range of flexibility in types which in their essence are invariable.