their present condition, have been formed by natural
selection, which acts solely by the preservation of useful modifications;
they have been retained, as we shall see, by inheritance, and relate to a
former condition of their possessor. It is difficult to know what are
nascent organs; looking to the future, we cannot of course tell how any
part will be developed, and whether it is now nascent; looking to the past,
creatures with an organ in a nascent condition will generally have been
supplanted and exterminated by their successors with the organ in a more
perfect and developed condition. The wing of the penguin is of high
service, and acts as a fin; it may, therefore, represent the nascent state
of the wings of birds; 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 is useless, and is truly rudimentary. The mammary glands of the
Ornithorhynchus may, perhaps, be considered, in comparison with the udder
of a cow, as in a nascent state. The ovigerous frena of certain cirripedes,
which are only slightly developed and which have ceased to give attachment
to the ova, are nascent branchiae.

Rudimentary organs in the individuals of the same species are very liable
to vary in degree of development {453} and in other respects. Moreover, in
closely allied species, the degree to which the same organ has been
rendered rudimentary occasionally differs much. This latter fact is well
exemplified in the state of the wings of the female moths in certain
groups. Rudimentary organs may be utterly aborted; and this implies, that
we find in an animal or plant no trace of an organ, which analogy would
lead us to expect to find, and which is occasionally found in monstrous
individuals of the species. Thus in the snapdragon (antirrhinum) we
generally do not find a rudiment of a fifth stamen; but this may sometimes
be seen. In tracing the homologies of the same part in different members of
a class, nothing is more common, or more necessary, than the use and
discovery of rudiments. This is well shown in the drawings given by Owen of
the bones of the leg 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 embryo, but
afterwards wholly disappear. It is also, I believe, a universal rule, that
a rudimentary part or organ is of greater size relatively to