Page:Popular Science Monthly Volume 24.djvu/595



AN has long been regarded not only as a compendium of the entire animal kingdom, but as an epitome of the universe—as Nature's short-hand expression of a long-continued history begun with the beginning condensation of the nebulae, and still going on to the development of higher types of humanity. Nature's language is hieroglyphic, and for the correct interpretation of her occult characters a key is necessary. It is one of the many triumphs of modern science that she has found at least a partial key to this mysterious book, and it is to the unlocking of some of its secrets that your attention is invited on this occasion.

My subject—the development of the human body from a microscopic speck of living matter—is a vast one, and the attempt to condense its consideration into the space of a single hour can result, at best, in a little more than a bare outline; but even such an exposition, however imperfect, may perhaps be deemed justifiable as a means of inciting to further study, and it is in this hope that the task is undertaken.

In the earliest perceptible stage of its existence, the human being consists of a minute apparently homogeneous mass of living matter of the kind known, since the days of Von Mohl and Remak, as protoplasm. The word means simply the first formative material, or the material in which all plants and animals have their origin. That it is a fact of natural history, and not a mere figment of the scientific imagination, that all plants and animals originate in a common substance, is no longer denied. This great principle was, indeed,