acquired strong jaws or talons. Cattle have acquired
a rough tongue and a rough palate to pull off the blades of grass, as
cows and sheep. Some birds have acquired harder beaks to crack nuts, as
the parrot. Others have acquired beaks to break the harder seeds, as
sparrows. Others for the softer kinds of flowers, or the buds of trees,
as the finches. Other birds have acquired long beaks to penetrate the
moister soils in search of insects or roots, as woodcocks, and others
broad ones to filtrate the water of lakes and to retain aquatic insects.
All which seem to have been gradually produced during many generations
_by the perpetual endeavour of the creature to supply the want of food,
and to have been delivered to their posterity with constant improvement
of them for the purposes required_.

"The third great want among animals is that of security, which seems to
have diversified the forms of their bodies and the colour of them; these
consist in the means of escaping other animals more powerful than
themselves. Hence some animals have acquired wings instead of legs, as
the smaller birds, for purposes of escape. Others, great length of fin
or of membrane, as the flying fish and the bat. Others have acquired
hard or armed shells, as the tortoise and the _Echinus marinus_.

"Mr. Osbeck, a pupil of Linnaeus, mentions the American frog-fish,
_Lophius Histrio_, which inhabits the large floating islands of sea-weed
about the Cape of Good Hope, and has fulcra resembling leaves, that the
fishes of prey may mistake it for the sea-weed, which it inhabits.[181]

"The contrivances for the purposes of security extend even to
vegetables, as is seen in the wonderful and various means of their
concealing or defending their honey from insects and their seeds from
birds. On the other hand, swiftness of wing has been acquired by hawks
and swallows to pursue their prey; and a proboscis of admirable
structure has been acquired by the bee, the moth, and the humming bird
for the purpose of plundering the nectaries of flowers. _All which seem
to have been formed by the original living filament, excited into action
by the necessities of the creatures which possess them_, and on which
their existence depends.

"From thus meditating on the great similarity of the structure of the
warm-blooded animals, and at the same time of the great changes they
undergo both before and after their nativity; and by considering in how
minute a portion of time many