Todd's 'Cyclopaedia of Anatomy' 1849-52, vol. iv. p. 1415. In man this
organ is only from three to six lines in length, but, like so many other
rudimentary parts, it is variable in development as well as in other
characters.) Some other rudimentary structures belonging to the
reproductive system might have been here adduced. (55. See, on this
subject, Owen, 'Anatomy of Vertebrates,' vol. iii. pp. 675, 676, 706.)

The bearing of the three great classes of facts now given is unmistakeable.
But it would be superfluous fully to recapitulate the line of argument
given in detail in my 'Origin of Species.' The homological construction of
the whole frame in the members of the same class is intelligible, if we
admit their descent from a common progenitor, together with their
subsequent adaptation to diversified conditions. On any other view, the
similarity of pattern between the hand of a man or monkey, the foot of a
horse, the flipper of a seal, the wing of a bat, etc., is utterly
inexplicable. (56. Prof. Bianconi, in a recently published work,
illustrated by admirable engravings ('La Theorie Darwinienne et la creation
dite independante,' 1874), endeavours to shew that homological structures,
in the above and other cases, can be fully explained on mechanical
principles, in accordance with their uses. No one has shewn so well, how
admirably such structures are adapted for their final purpose; and this
adaptation can, as I believe, be explained through natural selection. In
considering the wing of a bat, he brings forward (p. 218) what appears to
me (to use Auguste Comte's words) a mere metaphysical principle, namely,
the preservation "in its integrity of the mammalian nature of the animal."
In only a few cases does he discuss rudiments, and then only those parts
which are partially rudimentary, such as the little hoofs of the pig and
ox, which do not touch the ground; these he shews clearly to be of service
to the animal. It is unfortunate that he did not consider such cases as
the minute teeth, which never cut through the jaw in the ox, or the mammae