A Word About the Cells.
—The cell always possesses its three parts—membrane, protoplasm, and nucleus. But there is no rule as to the size or shape. Cells may be round or oblong, any shape. Substances pass in and out of the cell walls; and they are in motion, many of them, especially those that line the intestines and the air passages, and the white corpuscles of the blood. More than this, some cells, Dr. Jekyl-like, change their appearance and shape, send out finger-like bodies to catch enemies or food, and even travel all around in the body, often leaving it altogether.