CLASS I.—_Monera_ (single). These are the simplest forms of microscopic aquatic animals. They are entirely homogeneous, and without any developed organs; mere particles, of a jelly-like, but living, or life-supporting substance, called protoplasm, or more properly, bioplasm. This, all admit, is the physical basis of life, and the medium of its manifestation, just as the conductor is a medium of manifestation of electricity. But is it not a stupid blunder to confound the mere medium of its manifestation with the life itself? In neither case is the recognized physical basis of the manifestation necessary to the existence of that manifested by its means. Electricity exists without the conductor, and life may exist without the bioplasm. CLASS II.—_Gregarinida_ (living in herds). Minute animals which are found in the intestines of the lobster, clam, and cockroach. They are worm-like in form, and of a very simple, cell-like structure, the only organ being a nucleus. CLASS III.—_Rhizopoda_ (root footed). The representative forms of this class are the _Amœba_[1] and _Foraminifera_. The amœba is an indefinite little bit of bioplasm, as structureless as the monera, only that it is made up of two layers of the substance, has an apparent nucleus, and a contractile cavity within. These first animals vindicate their right to be recognized as such, by moving, receiving food, growing, and reproducing their kind. They move by a contractile force, throwing out at will processes of their soft bodies, to serve them as feet and arms. True, these are blunt, and without digits, but they answer the purpose. They eat either by simple absorption, or by wrapping their soft bodies around the food, and holding it in the extemporized stomach till it is, in some way, assimilated. The work of reproduction is carried on principally by self-division, and budding. The animal rends itself into two or more parts, each having all the elements of the whole, or it throws out buds that mature and drop from the parent mass, having the vital element, and a portion of the bioplasm, or medium necessary to its development. [Illustration: FORAMINIFERA, SHOWING ROOT-LIKE FEET.]