e theory of development, almost all the
higher forms of life must have existed during the Palaeozoic period. Thus,
from the fact that almost the whole of the Tertiary period has been
required to convert the ancestral Orohippus into the true horse, he
believes that, in order to have time for the much greater change of the
ancestral Ungulata into the two great odd-toed and even-toed divisions (of
which change there is no trace even among the earliest Eocene mammals), we
should require a large portion, if not the whole, of the Mesozoic or
Secondary period. Another case is furnished by the bats and whales, both of
which strange modifications of the {101} mammalian type occur perfectly
developed in the Eocene formation. What countless ages back must we then go
for the origin of these groups, the whales from some ancestral carnivorous
animal, and the bats from the insectivora! And even then we have to seek
for the common origin of carnivora, insectivora, ungulata, and marsupials
at a far earlier period; so that, on the lowest estimate, we must place the
origin of the mammalia very far back in Palaeozoic times. Similar evidence
is afforded by reptiles, of which Professor Huxley says: "If the very small
differences which are observable between the crocodiles of the older
Secondary formations and those of the present day furnish any sort of an
approximation towards an estimate of the average rate of change among
reptiles, it is almost appalling to reflect how far back in Palaeozoic
times we must go before we can hope to arrive at that common stock from
which the crocodiles, lizards, _Ornithoscelida_, and _Plesiosauria_, which
had attained so great a development in the Triassic epoch, must have been
derived." Professor Ramsay has expressed similar views, derived from a
general study of the whole series of geological formations and their
contained fossils. He says, speaking of the abundant, varied, and
well-developed fauna of the Cambrian period: "In this earliest known
_varied_ life we find no evidence of its having lived near the beginning of
the zoological series. In a broad sense, compared with what must have gone
before, both biologically and physically, all the phenomena connected with
this old period seem, to my mind, to be of quite a recent description; and
the climates of seas and lands were of the very same kind as those the
world enjoys at the present day."[31]

These opinions, and the facts on which they are founded, are