of the changes of animals above described
have been produced; would it be too bold to imagine that in the great
length of time since the earth began to exist, perhaps millions of ages
before the commencement of the history of mankind--would it be too bold
to imagine that all warm-blooded animals have arisen from one living
filament, which the Great First Cause endued with animality, with the
power of attaining new parts, attended with new propensities, directed
by irritations, sensations, volitions, and associations; and thus
possessing the faculty of continuing to improve, by its own inherent
activity, and of delivering down those improvements by generation to its
posterity world without end!

"Sixthly, the cold-blooded animals, as the fish tribes, which are
furnished with but one ventricle of the heart, and with gills instead of
lungs, and with fins instead of feet or wings, bear a great similarity
to each other; but they differ nevertheless so much in their general
structure from the warm-blooded animals, that it may not seem probable
at first view that the same living filament could have given origin to
this kingdom of animals, as to the former. Yet are there some creatures
which unite or partake of both these orders of animation, as the whales
and seals; and more particularly the frog, who changes from an aquatic
animal furnished with gills to an aerial one furnished with lungs.

"The numerous tribes of insects without wings, from the spider to the
scorpion, from the flea to the lobster; or with wings, from the gnat or
the ant to the wasp and the dragon-fly, differ so totally from each
other, and from the red-blooded classes above described, both in the
forms of their bodies and in their modes of life; besides the organ of
sense, which they seem to possess in their antennae or horns, to which
it has been thought by some naturalists that other creatures have
nothing similar; that it can scarcely be supposed that this nature of
animals could have been produced by the same kind of living filament as
the red-blooded classes above mentioned. And yet the changes which many
of them undergo in their early state to that of their maturity, are as
different as one animal can be from another. As those of the gnat, which
passes his early state in water, and then stretching out his new wings
and expanding his new lungs, rises in the air; as of the caterpillar and
bee-nymph, which feed on vegetable leaves or farina, and at lengt