bviously different from one another,
in faculty, in form, and in substance, than the various kinds of living
beings? What community of faculty can there be between the
brightly-coloured lichen, which so nearly resembles a mere mineral
incrustation of the bare rock on which it grows, and the painter, to
whom it is instinct with beauty, or the botanist, whom it feeds with
knowledge?

Again, think of the microscopic fungus--a mere infinitesimal ovoid
particle, which finds space and duration enough to multiply into
countless millions in the body of a living fly; and then of the wealth
of foliage, the luxuriance of flower and fruit, which lies between this
bald sketch of a plant and the giant pine of California, towering to the
dimensions of a cathedral spire, or the Indian fig, which covers acres
with its profound shadow, and endures while nations and empires come and
go around its vast circumference. Or, turning to the other half of the
world of life, picture to yourselves the great Finner whale, hugest of
beasts that live, or have lived, disporting his eighty or ninety feet of
bone, muscle, and blubber, with easy roll, among waves in which the
stoutest ship that ever left dockyard would flounder hopelessly; and
contrast him with the invisible animalcules--mere gelatinous specks,
multitudes of which could, in fact, dance upon the point of a needle
with the same ease as the angels of the Schoolmen could, in imagination.
With these images before your minds, you may well ask, what community of
form, or structure, is there between the animalcule and the whale; or
between the fungus and the fig-tree? And, _a fortiori_, between all
four?

Finally, if we regard substance, or material composition, what hidden
bond can connect the flower which a girl wears in her hair and the blood
which courses through her youthful veins; or, what is there in common
between the dense and resisting mass of the oak, or the strong fabric of
the tortoise, and those broad disks of glassy jelly which may be seen
pulsating through the waters of a calm sea, but which drain away to
mere films in the hand which raises them out of their element?

Such objections as these must, I think, arise in the mind of every one
who ponders, for the first time, upon the conception of a single
physical basis of life underlying all the diversities of vital
existence; but I propose to demonstrate to you that, notwithstanding
these apparent difficulties, a threefold unity