and pass away forever with the close of the period. Eurypterids
are common; stinging scorpions are abundant; and here occur the
first-known spiders.

We have seen that the arthropods were the first of all animals to
conquer the realm of the air, the earliest insects appearing in
the Ordovician. Insects had now become exceedingly abundant, and
the Carboniferous forests swarmed with the ancestral types of
dragon flies,--some with a spread of wing of more than two feet,--
May flies, crickets, and locusts. Cockroaches infested the swamps,
and one hundred and thirty-three species of this ancient order
have been discovered in the Carboniferous of North America. The
higher flower-loving insects are still absent; the reign of the
flowering plants has not yet begun. The Paleozoic insects were
generalized types connecting the present orders. Their fore wings
were still membranous and delicately veined, and used in flying;
they had not yet become thick, and useful only as wing covers, as
in many of their descendants.

FISHES still held to the Devonian types, with the exception that
the strange ostracoderms now had perished.

AMPHIBIANS. The vertebrates had now followed the arthropods and
the mollusks upon the land, and had evolved a higher type adapted
to the new environment. Amphibians--the class to which frogs and
salamanders belong--now appear, with lungs for breathing air and
with limbs for locomotion on the land. Most of the Carboniferous
amphibians were shaped like the salamander, with weak limbs
adapted more for crawling than for carrying the body well above
the ground. Some legless, degenerate forms were snakelike in