Page:George Archdall Reid 1896 The present evolution of man.djvu/43



has already been explained that the lowest organisms are probably quite beyond our ken. Higher organisms than these appear as minute and apparently formless specks, the protogenes of Haeckel, visible only under the highest powers of the microscope, and composed of that transparent jelly, "the formal basis of all life," which is known as protoplasm. About them also we have as yet been able to learn little beyond the fact that they are living beings. Higher in the scale are such organisms as the amœba; about them we are able to learn much that is important and instructive. They occupy that point in the scale of life at which the plant and animal kingdoms begin to diverge the one from the other, and though excessively minute, are larger than the protogenes, and therefore better observable. Each is a little mass of protoplasm in which may be seen a dot, the nucleus, which is usually situated eccentrically, and which, as modern research seems to have established, is the most important part of the organism. Such a speck of living protoplasm as the amoeba is known to biologists as a cell; and of such cells or variations of them the structures of all plants and animals are built up, a plant or animal composed of a single cell being known as a unicellular organism, whereas a plant or animal composed of a plurality of associated cells is known as a multicellular organism. Since such unicellular organisms as the amœba are fairly observable,