The former conviction that these two kingdoms were wholly different in structure, in function, and in kind of life, was not seriously disturbed by the difficulties which the naturalist encountered when he undertook to define them.

I accept extinction as best explaining disjoined species. I see that the same cause must have reduced many species of great range to small, and that it may have reduced large genera to so small, and of families.

I am sufficiently convinced already that the members of a profession know their own calling better than anyone else can know it.

The best opinion now is, that there are multitudinous forms which are not sufficiently differentiated to be distinctively either plant or animal, while, as respects ordinary plants and animals, the difficulty of laying down a definition has become far greater than ever before.

We have really, that I know of, no philosophical basis for high and low. Moreover, the vegetable kingdom does not culminate, as the animal kingdom does. It is not a kingdom, but a common-wealth; a democracy, and therefore puzzling and unaccountable from the former point of view.

This substance, which is manifold in its forms and protean in its transformations, has, in its state of living matter, one physiological name which has become familiar, that of protoplasm.

It was always understood that plants and animals, though completely contrasted in their higher representatives, approached each other very closely in their lower and simpler forms. But they were believed not to blend.