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 the species to their
conditions of life. That the mere physiological importance of an organ
does not determine its classificatory value, is almost shown by the one
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
at any group without being struck with this fact; and it has been most
fully acknowledged in the writings of almost every author. It will
suffice to quote the highest authority, Robert Brown, who in speaking
of certain organs in the Proteace , says their generic importance,
like that of all their parts, not only in this but, as I apprehend, in
every natural family, is very unequal, and in some cases seems to be
entirely lost. Again in another work he says, the genera of the
Connarace differ in having one or more ovaria, in the existence or
absence of albumen, in the imbricate or valvular stivation. 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 insects, in
one great division of the Hymenoptera, the antenn , as Westwood has
remarked, are most constant in structure;
in another division they differ much, and the differences are of quite
subordinate value in classification; yet no one probably will say that
the antenn in these two divisions of the same order are of unequal
physiological importance. Any number of instances could be given of the
varying importance for classification of the same important organ
within the same group of beings.
Again, no one will say that rudimentary or atrophied organs are of high
physiological or vital importance; yet, undoubtedly, organs in this
condition are often of high value in classification. No one will
dispute that the rudimentary teeth in the upper jaws of young
ruminants, and certain rudimentary bones of the leg, are highly
serviceable in exhibiting the close affinity between Ruminants and
Pachyderms. Robert Brown has strongly insisted on the fact that the
rudimentary florets are of the highest importance in the classification
311