ays be somewhat rare; for beings thus
provided will commonly have been supplanted by their successors with the
same organ in a more perfect state, and consequently will have become
long ago extinct. The wing of the penguin is of high service, acting as
a fin; it may, therefore, represent the nascent state of the wing: not
that I believe this to be the case; it is more probably a reduced organ,
modified for a new function: the wing of the Apteryx, on the other hand,
is quite useless, and is truly rudimentary. Owen considers the simple
filamentary limbs of the Lepidosiren as the "beginnings of organs
which attain full functional development in higher vertebrates;" but,
according to the view lately advocated by Dr. Gunther, they are probably
remnants, consisting of the persistent axis of a fin, with the lateral
rays or branches aborted. The mammary glands of the Ornithorhynchus may
be considered, in comparison with the udders of a cow, as in a nascent
condition. The ovigerous frena of certain cirripedes, which have ceased
to give attachment to the ova and are feebly developed, are nascent
branchiae.

Rudimentary organs in the individuals of the same species are very
liable to vary in the degree of their development and in other respects.
In closely allied species, also, the extent to which the same organ
has been reduced occasionally differs much. This latter fact is well
exemplified in the state of the wings of female moths belonging to
the same family. Rudimentary organs may be utterly aborted; and this
implies, that in certain animals or plants, parts are entirely absent
which analogy would lead us to expect to find in them, and which
are occasionally found in monstrous individuals. Thus in most of
the Scrophulariaceae the fifth stamen is utterly aborted; yet we may
conclude that a fifth stamen once existed, for a rudiment of it is found
in many species of the family, and this rudiment occasionally becomes
perfectly developed, as may sometimes be seen in the common snap-dragon.
In tracing the homologies of any part in different members of the same
class, nothing is more common, or, in order fully to understand the
relations of the parts, more useful than the discovery of rudiments.
This is well shown in the drawings given by Owen of the leg bones of the
horse, ox, and rhinoceros.

It is an important fact that rudimentary organs, such as teeth in the
upper jaws of whales and ruminants, can often be detected in the embry