probably speechless, inasmuch as the tubercle in existing man gives
attachment to muscles of the tongue. From the latter it has been argued
that all the valves in the veins of the human body have reference, in
their disposition, to the incidence of blood-pressure when the attitude
of the body is horizontal, or quadrupedal. Now, the former case has
already broken down, and I find that the latter does not hold. But we
can well afford to lose such doubtful and spurious cases, in view of all
the foregoing unquestionable and genuine cases of vestigial structures
which are to be met with even within the limits of our own
organization--and even when these limits are still further limited by
selecting only those instances which refer to the very latest chapter of
our long ancestral history.

CHAPTER IV.

EMBRYOLOGY.

We will next consider what of late years has become the most important
of the lines of evidence, not only in favour of the general fact of
evolution, but also of its history: I mean the evidence which has been
yielded by the newest of the sciences, the science of Embryology. But
here, as in the analogous case of adult morphology, in order to do
justice to the mass of evidence which has now been accumulated, a whole
volume would be necessary. As in that previous case, therefore, I must
restrict myself to giving an outline sketch of the main facts.

First I will display what in the language of Paley we may call "the
state of the argument."

It is an observable fact that there is often a close correspondence
between developmental changes as revealed by any chronological series of
fossils which may happen to have been preserved, and developmental
changes which may be observed during the life-history of now existing
individuals belonging to the same group of animals. For instance, the
successive development of prongs in the horns of deer-like animals,
which is so clearly shown in the geological history of this tribe, is
closely reproduced in the life-history of existing deer. Or, in other
words, the antlers of an existing deer furnish in their development a
kind of _resume_, or recapitulation, of the successive phases whereby
the primitive horn was gradually superseded by horns presenting a
greater and greater number of prongs in successive species of extinct
deer (Fig. 26). Now it must be obvious that such a recapitulation in the
life-history of an existing animal of developmental changes successively
dis