176-198.]
[Footnote 42: See Kerner's _Flowers and their Unbidden Guests_ for
numerous other structures and peculiarities of plants which are shown to
be adaptive and useful.]
[Footnote 43: _Nature_, vol. xx. p. 603.]
[Footnote 44: _Nature_, vol. xxxviii. p. 328.]
[Footnote 45: A very remarkable illustration of function in an
apparently useless ornament is given by Semper. He says, "It is known
that the skin of reptiles encloses the body with scales. These scales
are distinguished by very various sculpturings, highly characteristic of
the different species. Irrespective of their systematic significance
they appear to be of no value in the life of the animal; indeed, they
are viewed as ornamental without regard to the fact that they are
microscopic and much too delicate to be visible to other animals of
their own species. It might, therefore, seem hopeless to show the
necessity for their existence on Darwinian principles, and to prove that
they are physiologically active organs. Nevertheless, recent
investigations on this point have furnished evidence that this is
possible.
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