world only by the frogs, the toads,
the newts, and the axolotls. Here we must certainly with shame confess
that the amphibians of old greatly surpassed their degenerate
descendants in our modern waters. The Japanese salamander, by far the
biggest among our existing newts, never exceeds a yard in length from
snout to tail; whereas some of the labyrinthodonts (forgive me once
more) of the Carboniferous Epoch must have reached at least seven or
eight feet from stem to stern. But the reason of this falling off is not
far to seek. When the adventurous newts and frogs of that remote period
first dropped their gills and hopped about inquiringly on the dry land,
under the shadow of the ancient tree-ferns and club-mosses, they were
the only terrestrial vertebrates then existing, and they had the field
(or, rather, the forest) all to themselves. For a while, therefore, like
all dominant races for the time being, they blossomed forth at their
ease into relatively gigantic forms. Frogs as big as donkeys, and efts
as long as crocodiles, luxuriated to their hearts' content in the marshy
lowlands, and lorded it freely over the small creatures which they found
in undisturbed possession of the Carboniferous isles. But as ages passed
away, and new improvements were slowly invented and patented by survival
of the fittest in the offices of nature, their own more advanced and
developed descendants, the reptiles and mammals, got the upper hand
with them, and soon lived them down in the struggle for life, so that
this essentially intermediate form is now almost entirely restricted to
its one adapted seat, the pools and ditches that dry up in summer.

The reptiles, again, are a class in which the biggest modern forms are
simply nowhere beside the gigantic extinct species. First appearing on
the earth at the very close of the vast primary periods--in the Permian
age--they attained in secondary times the most colossal proportions, and
have certainly never since been exceeded in size by any later forms of
life in whatever direction. But one must remember that during the heyday
of the great saurians, there were as yet no birds and no mammals. The
place now filled in the ocean by the whales and grampuses, as well as
the place now filled in the great continents by the elephants, the
rhinoceroses, the hippopotami, and the other big quadrupeds, was then
filled exclusively by huge reptiles, of the sort rendered familiar to us
all by the restored effigi