of male quadrupeds, or the wings of certain beetles, existing under the
soldered wing-covers, or the vestiges of the pistil and stamens in various
flowers, and many other such cases. Although I greatly admire Prof.
Bianconi's work, yet the belief now held by most naturalists seems to me
left unshaken, that homological structures are inexplicable on the
principle of mere adaptation.) It is no scientific explanation to assert
that they have all been formed on the same ideal plan. With respect to
development, we can clearly understand, on the principle of variations
supervening at a rather late embryonic period, and being inherited at a
corresponding period, how it is that the embryos of wonderfully different
forms should still retain, more or less perfectly, the structure of their
common progenitor. No other explanation has ever been given of the
marvellous fact that the embryos of a man, dog, seal, bat, reptile, etc.,
can at first hardly be distinguished from each other. In order to
understand the existence of rudimentary organs, we have only to suppose
that a former progenitor possessed the parts in question in a perfect
state, and that under changed habits of life they became greatly reduced,
either from simple disuse, or through the natural selection of those
individuals which were least encumbered with a superfluous part, aided by
the other means previously indicated.

Thus we can understand how it has come to pass that man and all other
vertebrate animals have been constructed on the same general model, why
they pass through the same early stages of development, and why they retain
certain rudiments in common. Consequently we ought frankly to admit their
community of descent: to take any other view, is to admit that our own
structure, and that of all the animals around us, is a mere snare laid to
entrap our judgment. This conclusion is greatly strengthened, if we look
to the members of the whole animal series, and consider the evidence
derived from their affinities or classification, their geographical