followed out so as to agree with all the phaenomena presented by
organized beings, their extinction and succession in past ages, and all
the extraordinary modifications of form, instinct and habits which they
exhibit.

III.

MIMICRY, AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS.

There is no more convincing proof of the truth of a comprehensive
theory, than its power of absorbing and finding a place for new facts,
and its capability of interpreting phaenomena which had been previously
looked upon as unaccountable anomalies. It is thus that the law of
universal gravitation and the undulatory theory of light have become
established and universally accepted by men of science. Fact after fact
has been brought forward as being apparently inconsistent with them, and
one after another these very facts have been shown to be the
consequences of the laws they were at first supposed to disprove. A
false theory will never stand this test. Advancing knowledge brings to
light whole groups of facts which it cannot deal with, and its advocates
steadily decrease in numbers, notwithstanding the ability and scientific
skill with which it may have been supported. The great name of Edward
Forbes did not prevent his theory of "Polarity in the distribution of
Organic beings in Time" from dying a natural death; but the most
striking illustration of the behaviour of a false theory is to be found
in the "Circular and Quinarian System" of classification propounded by
MacLeay, and developed by Swainson, with an amount of knowledge and
ingenuity that have rarely been surpassed. This theory was eminently
attractive, both from its symmetry and completeness, and from the
interesting nature of the varied analogies and affinities which it
brought to light and made use of. The series of Natural History volumes
in "Lardner's Cabinet Cyclopaedia," in which Mr. Swainson developed it in
most departments of the animal kingdom, made it widely known; and in
fact for a long time these were the best and almost the only popular
text-books for the rising generation of naturalists. It was favourably
received too by the older school, which was perhaps rather an indication
of its unsoundness. A considerable number of well-known naturalists
either spoke approvingly of it, or advocated similar principles, and for
a good many years it was decidedly in the ascendent. With such a
favourable introduction, and with such talented exponents, it must have
become