nized by Harvey, and first expressed in his famous aphorism, "Omne vivum ex ovo"—an egg, whenever it occurs, consisting essentially of a minute globule of protoplasm.
What is the origin of this universal, white-of-egg-like material? As little is known of the history of the first production of protoplasm as of that of the elements—hydrogen, oxygen, nitrogen, carbon, etc., of which it is composed. So far as yet discovered, all protoplasm, whether vegetable or animal, is derived from pre-existing protoplasm. The spontaneous production of living matter from non-living materials has never been satisfactorily proved. The particular kind of protoplasm which we are about to consider—viz., the human germ—is the combined derivative of certain glands which exist in separate adult human beings who represent the opposite sexual polarities belonging to all except the lowest vegetable and animal types. At the earliest recognizable stage of his existence man may therefore be regarded, physiologically, as a secretion. Zoölogically, to what rank is he, then, entitled? The undeveloped human ovum, immediately after its fertilization, corresponds in structure to the lowest known order of the most simple class of animals, the Protozoa, which stand at the very foot of the zoölogical scale. To this most humble of all known living creatures Professor Haeckel has given the name of Moner, a word of the same origin as monad, and expressive of ultimate simplicity and primitiveness.
More simple even than the moner, however, is the bathybius, found on the deep-sea bottom, and described by Professor Huxley as consisting of an ill-defined mass of a slime-like material possessing all the properties of living protoplasm. Even granting with skeptics on this point that the existence of bathybius is not satisfactorily proved, we may nevertheless assert with confidence that, as the natural predecessor of the moner, it ought to exist, and will some time be discovered, just as certain unobserved heavenly bodies have been partially described and located by astronomers long before the telescope had penetrated the obscurity in which they were hidden.
Through the processes of nutrition, under the combined influences of growth and development, this non-nucleated mass of living protoplasm (the human ovum) acquires a nucleus; in other words, there appears at its center a minute speck of matter slightly more opaque than the surrounding matter. Differentiation has therefore begun; that is, a difference of parts has made its appearance. How does this nucleus (to which, in cell-physiology, so much importance is attached) differ from the surrounding: matter which constitutes the bulk of the germ? Chemically, it is more active; it is believed to be the part where nutrition (the assimilation of new material) mainly takes place. Its greater chemical, and, therefore, nutritive activity, is shown by its deeper staining with coloring-matters, such as carmine and hæmatoxylin, and by the fact that, with the access of nutriment, fresh nu-
