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 always 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.
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