with the glassblower in her dealings with the cell.
The artisan blows his vitreous bubbles, large or small, to be used
afterwards as may be wanted. So Nature shapes her hyaline vesicles and
modifies them to serve the needs of the part where they are found. The
artisan whirls his rod, and his glass bubble becomes a flattened disk,
with its bull's-eye for a nucleus. These lips of ours are all glazed
with microscopic tiles formed of flattened cells, each one of them with
its nucleus still as plain and relatively as prominent, to the eye of the
microscopist, as the bull's-eye in the old-fashioned windowpane.
Everywhere we find cells, modified or unchanged. They roll in
inconceivable multitudes (five millions and more to the cubic millimetre,
according to Vierordt) as blood-disks through our vessels. A
close-fitting mail of flattened cells coats our surface with a panoply of
imbricated scales (more than twelve thousand millions), as Harting has
computed, as true a defence against our enemies as the buckler of the
armadillo or the carapace of the tortoise against theirs. The same
little protecting organs pave all the great highways of the interior
system. Cells, again, preside over the chemical processes which
elaborate the living fluids; they change their form to become the agents
of voluntary and involuntary motion; the soul itself sits on a throne of
nucleated cells, and flashes its mandates through skeins of glassy
filaments which once were simple chains of vesicles. And, as if to
reduce the problem of living force to its simplest expression, we see the
yolk of a transparent egg dividing itself in whole or in part, and again
dividing and subdividing, until it becomes a mass of cells, out of which
the harmonious diversity of the organs arranges itself, worm or man, as
God has willed from the beginning.

This differentiation having been effected, each several part assumes its
special office, having a life of its own adjusted to that of other parts
and the whole. "Just as a tree constitutes a mass arranged in a definite
manner, in which, in every single part, in the leaves as in the root, in
the trunk as in the blossom, cells are discovered to be the ultimate
elements, so is it also with the forms of animal life. Every animal
presents itself as a sum of vital unities, every one of which manifests
all the characteristics of life."

The mechanism is as clear, as unquestionable, as absolutely settled and
universally accepted,