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they may be for the welfare of the being in relation to the outer world. Perhaps from this cause it has partly arisen, that almost all naturalists lay the greatest stress on resemblances in organs of high vital or physiological importance. No doubt this view of the classificatory importance of organs which are important is generally, but by no means always, true. But their importance for classification, I believe, depends on their greater constancy throughout large groups of species; and this constancy depends on such organs having generally been subjected to less change in the adaptation of
species to their conditions of life. That the mere physiological importance of an organ does not determine its classificatory value, is almost
by the
fact, that in allied groups, in which the same organ, as we have every reason to suppose, has nearly the same physiological value, its classificatory value is widely different. No naturalist can have worked
any group without being struck with this fact; and it has been
fully acknowledged in the writings of almost every author. It will suffice to quote the highest authority, Robert Brown,
in speaking of certain organs in the
says their generic importance, "like that of all their parts, not only in
but, as I apprehend, in every natural family, is very unequal, and in some cases seems to be entirely lost."
in another work he says, the genera of the Connaraceæ "differ in having one or more ovaria, in the existence or absence of albumen, in the imbricate or valvular æstivation. Any one of these characters singly is frequently of more than generic importance, though here even when all taken together they appear insufficient to separate Cnestis from Connarus." To give an example amongst
in one great division of the Hymenoptera, the antennæ, as Westwood has remarked, are most constant in structure;
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