Our modern tailless Amphibia, frogs and toads, appear much later
in the story of the earth, but they are not without interest here
on account of the remarkable capacity which they show to adapt
themselves to different surroundings. There are frogs, like the
tree-frog of Martinique, and others in regions where water is
scarce, which never pass through the tadpole stage; or, to be
quite accurate, they lose the gills and tail in the egg, as
higher land-animals do. On the other hand, there is a modern
Amphibian, the axolotl of Mexico, which retains the gills
throughout life, and never lives on land. Dr. Gadow has shown
that the lake in which it lives is so rich in food that it has
little inducement to leave it for the land. Transferred to a
different environment, it may pass to the land, and lose its
gills. These adaptations help us to understand the rich variety
of Amphibian forms that appeared in the changing conditions of
the Carboniferous world.
When we think of the diet of the Amphibia we are reminded of the
other prominent representatives of land life at the time. Snails,
spiders, and myriapods crept over the ground or along the stalks
of the trees, and a vast population of insects filled the air.
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