ites of
certain cirripedes, when adult, and yet no one dreams of separating them.
The naturalist includes as one species the several larval stages of the
same individual, however much they may differ from each other and from the
adult; as he likewise includes the so-called alternate generations of
Steenstrup, which can only in a technical sense be considered as the same
individual. He includes monsters; he includes varieties, not solely because
they closely resemble the parent-form, but because they are descended from
it. He who believes that the cowslip is descended from the primrose, or
conversely, ranks them together as a single species, and gives a single
definition. As soon as three Orchidean forms (Monochanthus, Myanthus, and
Catasetum), which had previously been ranked as three distinct genera, were
known to be sometimes produced on the same spike, they were immediately
included as a single species. {425}

As descent has universally been used in classing together the individuals
of the same species, though the males and females and larvae are sometimes
extremely different; and as it has been used in classing varieties which
have undergone a certain, and sometimes a considerable amount of
modification, may not this same element of descent have been unconsciously
used in grouping species under genera, and genera under higher groups,
though in these cases the modification has been greater in degree, and has
taken a longer time to complete? I believe it has thus been unconsciously
used; and only thus can I understand the several rules and guides which
have been followed by our best systematists. We have no written pedigrees;
we have to make out community of descent by resemblances of any kind.
Therefore we choose those characters which, as far as we can judge, are the
least likely to have been modified in relation to the conditions of life to
which each species has been recently exposed. Rudimentary structures on
this view are as good as, or even sometimes better than, other parts of the
organisation. We care not how trifling a character may be--let it be the
mere inflection of the angle of the jaw, the manner in which an insect's
wing is folded, whether the skin be covered by hair or feathers--if it
prevail throughout many and different species, especially those having very
different habits of life, it assumes high value; for we can account for its
presence in so many forms with such different habits, only by its
inh