never lives in the water. Yet if
we open a gravid female, we find tadpoles inside her with exquisitely
feathered gills; and when placed in water they swim about like the
tadpoles of the water-newt. Obviously this aquatic organisation has no
reference to the future life of the animal, nor has it any adaptation
to its embryonic condition; it has solely reference to ancestral
adaptations, it repeats a phase in the development of its progenitors."

An organ, serving for two purposes, may become rudimentary or utterly
aborted for one, even the more important purpose, and remain perfectly
efficient for the other. Thus, in plants, the office of the pistil is
to allow the pollen-tubes to reach the ovules within the ovarium.
The pistil consists of a stigma supported on the style; but in some
Compositae, the male florets, which of course cannot be fecundated, have
a rudimentary pistil, for it is not crowned with a stigma; but the style
remains well developed and is clothed in the usual manner with hairs,
which serve to brush the pollen out of the surrounding and conjoined
anthers. Again, an organ may become rudimentary for its proper purpose,
and be used for a distinct one: in certain fishes the swim-bladder seems
to be rudimentary for its proper function of giving buoyancy, but has
become converted into a nascent breathing organ or lung. Many similar
instances could be given.

Useful organs, however little they may be developed, unless we have
reason to suppose that they were formerly more highly developed, ought
not to be considered as rudimentary. They may be in a nascent condition,
and in progress towards further development. Rudimentary organs, on
the other hand, are either quite useless, such as teeth which never cut
through the gums, or almost useless, such as the wings of an ostrich,
which serve merely as sails. As organs in this condition would formerly,
when still less developed, have been of even less use than at present,
they cannot formerly have been produced through variation and
natural selection, which acts solely by the preservation of useful
modifications. They have been partially retained by the power of
inheritance, and relate to a former state of things. It is, however,
often difficult to distinguish between rudimentary and nascent organs;
for we can judge only by analogy whether a part is capable of further
development, in which case alone it deserves to be called nascent.
Organs in this condition will alw