it,
these critics maintained that he was making too great a demand upon the
argument from ignorance--that, even allowing for the imperfection of the
record, they would certainly have expected at least a few cases of
testimony to _specific_ transmutation. For, they urged in effect,
looking to the enormous profusion of the extinct species on the one
hand, and to the immense number of known fossils on the other, it was
incredible that no satisfactory instances of specific transmutation
should ever have been brought to light, if such transmutation had ever
occurred in the universal manner which the theory was bound to suppose.
But since Darwin first published his great work palaeontologists have
been very active in discovering and exploring fossiliferous beds in
sundry parts of the world; and the result of their labours has been to
supply so many of the previously missing links that the voice of
competent criticism in this matter has now been well-nigh silenced.
Indeed, the material thus furnished to an advocate of evolution at the
present time is so abundant that his principal difficulty is to select
his samples. I think, however, that the most satisfactory result will be
gained if I restrict my exposition to a minute account of some few
series of connecting links, rather than if I were to take a more general
survey of a larger number. I will, therefore, confine the survey to the
animal kingdom, and there mention only some of the cases which have
yielded well-detailed proof of continuous differentiation.

It is obvious that the parts of animals most likely to have been
preserved in such a continuous series of fossils as the present line of
evidence requires, would have been the hard parts. These are horns,
bones, teeth, and shells. Therefore I will consider each of these four
classes of structures separately.

* * * * *

Horns wherever they occur, are found to be of high importance for
purposes of classification. They are restricted to the Ruminants, and
appear under three different forms or types--namely solid, as in
antelopes; hollow, as in sheep; and deciduous, as in deer. Now, in each
of these divisions we have a tolerably complete palaeontological history
of the evolution of horns. The early ruminants were altogether hornless
(Fig. 60). Then, in the middle Miocene, the first antelopes appeared
with tiny horns, which progressively increased in size among the
ever-multiplying species o