r, it seems to me that
nothing is thus added to our knowledge. Such expressions as that
famous one of Linnaeus, 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