If we allow, with Pictet, that Darwin’s theory will very well serve for all that concerns the present epoch of the world’s history,—­an epoch which this renowned palaeontologist regards as including the diluvial or quaternary period,—­then Darwin’s first and foremost need in his onward course is a practicable road from this into and through the tertiary period, the intervening region between the comparatively near and the far remote past.  Here Lyell’s doctrine paves the way, by showing that in the physical geology there is no general or absolute break between the two, probably no greater between the latest tertiary and the quaternary period than between the latter and the present time.  So far, the Lyellian view is, we suppose, generally concurred in.  Now as to the organic world, it is largely admitted that numerous tertiary species have continued down into the quaternary, and many of them to the present time.  A goodly percentage of the earlier and nearly half of the later tertiary mollusca, according to Des Hayes, Lyell, and, if we mistake not, Bronn, still live.  This identification, however, is now questioned by a naturalist of the very highest authority.  But, in its bearings on the new theory, the point here turns not upon absolute identity so much as upon close resemblance.  For those who, with Agassiz, doubt the specific identity in any of these cases, and those who say, with Pictet, that “the later tertiary deposits contain in general the debris of species very nearly related to those which still exist, belonging to the same genera, but specifically different,” may also agree with Pictet that the nearly related species of successive faunas must or may have had “a material connection.”  Now the only material connection that we have an idea of in such a case is a genealogical one.  And the supposition of a genealogical connection is surely not unnatural in such cases,—­is demonstrably the natural one as respects all those tertiary species which experienced naturalists have pronounced to be identical with existing ones, but which others now deem distinct.  For to identify the two is the same thing as to conclude the one to be the ancestors of the other.  No doubt there are differences between the tertiary and the present individuals, differences equally noted by both classes of naturalists, but differently estimated.  By the one these are deemed quite compatible, by the other incompatible, with community of origin.  But who can tell us what amount of difference is compatible with community of origin?  This is the very question at issue, and one to be settled by observation alone.  Who would have thought that the peach and the nectarine came from one stock?  But, this being proved, is it now very improbable that both were derived from the almond, or from some common amygdaline progenitor?  Who would have thought that the cabbage, cauliflower, broccoli, kale, and kohlrabi are derivatives of one species, and rape or colza, turnip, and probably rutabaga,