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 embryo, but
afterwards wholly disappear. It is also, I believe, a universal rule, that
a rudimentary part is of greater size in the embryo relatively to the
adjoining parts, than in the adult; so that the organ at this early age is
less rudimentary, or even cannot be said to be in any degree rudimentary.
Hence rudimentary organs in the adult are often said to have retained their
embryonic condition.
I have now given the leading facts with respect to rudimentary organs. In
reflecting on them, every one must be struck with astonishment; for the
same reasoning power which tells us that most parts and organs are
exquisitely adapted for certain purposes, tells us with equal plainness
that these rudimentary or atrophied organs are imperfect and useless. In
works on natural history, rudimentary organs are generally said to have
been created "for the sake of symmetry," or in order "to complete the
scheme of nature." But this is not an explanation, merely a restatement of
the fact. Nor is it consistent with itself: thus the boa-constrictor has
rudiments of hind limbs and of a pelvis, and if it be said that these bones
have been retained "to complete the scheme of nature," why, as Professor
Weismann asks, have they not been retained by other snakes, which do not
possess even a vestige of these same bones? What would be thought of an
astronomer who maintained that the satellites revolve in elliptic courses
round their planets "for the sake of symmetry," because the planets thus
revolve round the sun? An eminent physiologist accounts for the presence
of rudimentary organs, by supposing that they serve to excrete matter in
excess, or matter injurious to the system; but can we suppose that the
minute papilla, which often represents the pistil in male flowers, and
which is formed of mere cellular tissue, can thus act? Can we suppose that
rudimentary teeth, which are subsequently absorbed, are beneficial to the
rapidly growing embryonic calf by removing matter so precious as phosphate
of lime? When a man's fingers have been amputated, imperfect nails have
been known to appear on the stumps, and I could as soon believe that these
vestiges of nails are developed in order to excrete horny matter, as that
the rudimentary nails on the fin of the manatee have been developed for
this same purpose.
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