one of Linn us, and which we often meet with in a more or less
concealed form, that the characters do not make the genus, but that the
genus gives the characters, seem to imply that something more is
included in our classification, than mere resemblance. I believe that
something more is included; and that propinquity of descent, the only
known cause of the similarity of organic beings, is the bond, hidden as
it is by various degrees of modification,
which is partially revealed to us by our classifications.
Let us now consider the rules followed in classification, and the
difficulties which are encountered on the view that classification
either gives some unknown plan of creation, or is simply a scheme for
enunciating general propositions and of placing together the forms most
like each other. It might have been thought (and was in ancient times
thought) that those parts of the structure which determined the habits
of life, and the general place of each being in the economy of nature,
would be of very high importance in classification. Nothing can be more
false. No one regards the external similarity of a mouse to a shrew, of
a dugong to a whale, of a whale to a fish, as of any importance. These
resemblances, though so intimately connected with the whole life of the
being, are ranked as merely adaptive or analogical characters; but to
the consideration of these resemblances we shall have to recur. It may
even be given as a general rule, that the less any part of the
organisation is concerned with special habits, the more important it
becomes for classification. As an instance: Owen, in speaking of the
dugong, says, The generative organs being those which are most
remotely related to the habits and food of an animal, I have always
regarded as affording very clear indications of its true affinities. We
are least likely in the modifications of these organs to mistake a
merely adaptive for an essential character. So with plants, how
remarkable it is that the organs of vegetation, on which their whole
life depends, are of little signification, excepting in the first main
divisions; whereas the organs of reproduction, with their product the
seed, are of paramount importance!
We must not, therefore, in classifying, trust to resemblances in parts
of the organisation, however important
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
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