As we have seen Nature anticipating the plasterer in fibro-cartilage, so we see her beforehand 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, as the order of movement of the heavenly bodies, which we compute backward to the days of the observatories on the plains of Shinar, and on the faith of which we regulate the movements of war and trade by the predictions of our ephemeris.