it were, so interwoven throughout the organic world, and because there
is, in consequence, so much difficulty in following them, that
artificial systems have to be made in the first instance as feelers
towards eventual discovery of the natural system. In other words, while
forming their artificial systems of classification, it has always been
the aim of naturalists--whether consciously or unconsciously--to admit
as the bases of their systems those characters which, in the then state
of their knowledge, seemed most calculated to play an important part in
the eventual construction of the natural system. If we were dealing with
the history of classification, it would here be interesting to note how
the course of it has been marked by gradual change in the principles
which naturalists adopted as guides to the selection of characters on
which to found their attempts at a natural classification. Some of these
changes, indeed, I shall have to mention later on; but at present what
has to be specially noted is, that through all these changes of theory
or principle, and through all the ever-advancing construction of their
taxonomic science, naturalists themselves were unable to give any
intelligible reason for the faith that was in them--or the faith that
over and above the artificial classifications which were made for the
mere purpose of cataloguing the living library of organic nature, there
was deeply hidden in nature itself a truly natural classification, for
the eventual discovery of which artificial systems might prove to be of
more or less assistance.

Linnaeus, for example, expressly says--"You ask me for the characters of
the natural orders; I confess that I cannot give them." Yet he maintains
that, although he cannot define the characters, he knows, by a sort of
naturalist's instinct, what in a general way will subsequently be found
to be the organs of most importance in the eventual grouping of plants
under a natural system. "I will not give my reasons for the distribution
of the natural orders which I have published," he said: "you, or some
other person, after twenty or after fifty years, will discover them, and
see that I was right."

Thus we perceive that in forming their provisional or artificial
classifications, naturalists have been guided by an instinctive belief
in some general principle of natural affinity, the character of which
they have not been able to define; and that the structures which they
selected