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 organs whatever, except the cilia just spoken of. The same is true of several of the Infusoria; for you must know that naturalists no longer recognize the complex organization which Ehrenberg fancied he had detected in these microscopic beings. If it pains you to relinquish the piquant notion of a microscopic animalcule having a structure equal in complexity to that of the elephant, there will be ample compensation in the notion which replaces it, the notion of an ascending series of animal organisms, rising from the structureless amœba to the complex frame of a mammal. On a future occasion we shall see that, great as Ehrenberg's services have been, his interpretations of what he saw have one by one been replaced by truer notions. His immense class of Infusoria has been, and is constantly being, diminished; many of his animals turn out to be plants; many of them embryos of worms; and some of them belong to the same divisions of the animal kingdom as the oyster and the shrimp: that is to say, they range with the Molluscs and Crustaceans. In these, of course, there is a complex organization; but in the Infusoria, as now understood, the organization is extremely simple. No one now believes the clear spaces visible in their substance to be stomachs, as Ehrenberg believed; and the idea of the Polygastrica, or many-stomached Infusoria, is abandoned. No one believes the coloured specs to be eyes; because, not to mention the difficulty of conceiving eyes where there is no nervous system, it has been found that even the spores of some plants have these coloured specs; and they are assuredly not eyes. If, then, we exclude the highly-organized Rotifera, or "Wheel Animalcules," which are genuine Crustacea, we may say that all Infusoria, whether they be the young of worms or not, are of very simple organization.

And this leads us to consider what biologists mean by an organ: it is a particular portion of the body set apart for the performance of some particular function. The whole process of development is this setting apart for special purposes. The starting-point of Life is a single cell—that is to say, a microscopic sac, filled with liquid and granules, and having within it a nucleus, or smaller sac. Paley has somewhere remarked, that in the early stages, there is no difference discernible between a frog and a philosopher. It is very true; truer than he conceived. In the earliest stage of all, both the Batrachian and the Philosopher are nothing but single cells; although the one cell will develop into an Aristotle or a Newton, and the other will get no higher than the cold, damp, croaking animal which boys will pelt, anatomists dissect, and Frenchmen eat. From the starting-point of a single cell, this is the course taken: the cell divides itself into two, the two become four, the four eight, and so on, till a mass of cells is formed, not unlike the shape of a mulberry. This mulberry-mass then becomes a sac, with double envelopes, or walls: the inner wall, turned towards the yelk, or food, becomes the assimilating surface for the whole; the outer wall, turned towards the surrounding medium, becomes the surface which is to bring frog and philosopher into contact and relation with the external world—the Non-Ego, as the philosopher, in after life, will