This family, because of its even number of toes and the habit of chewing the cud, resembles the camel family, the deer family, and several other families. These are all placed together in the next higher systematic unit called an _order_, in this case, the order of _ruminants_. The ruminants, because they are covered with hair and nourish the young with milk, are in every essential respect related to the one-toed horses, the beasts of prey, the apes, etc. Hence they are all placed in a more inclusive division of animals, the _class_ called _mammals_. All mammals have the skeleton, or support of the body, on the inside, the axis of which is called the vertebral column. This feature also belongs to the classes of reptiles, amphibians, and fishes. It is therefore consistent to unite these classes by a general idea or conception into a great _branch_ of animals called the _vertebrates_. Returning from the general to the particular by successive steps, state the branch, class, order, family, genus, and species to which the cow belongs. =The Eight Branches or Sub-kingdoms.=—The simplest classification divides the whole animal kingdom into eight branches, named and characterized as follows, beginning with the lowest: I. PROTOZOANS. One-celled. II. SPONGES. Many openings. III. POLYPS. Circular; cuplike; having only one opening which is both mouth and vent. IV. ECHINODERMS. Circular; rough-skinned; two openings. V. MOLLUSCS. No skeleton; usually with external shell. VI. VERMES. Elongate body, no jointed legs. VII. ARTHROPODS. External jointed skeleton; jointed legs. VIII. VERTEBRATES. Internal jointed skeleton with axis or backbone.[1] Footnote 1: This is the briefest classification. Animals have also been divided into twelve branches. The naming of animals is somewhat chaotic at present, but an attempt to come to an agreement is now being made by zoologists of all nations. CHAPTER II PROTOZOA (One-celled Animals) THE AMŒBA SUGGESTIONS.—Amœbas live in the slime found on submerged stems and leaves in standing water, or in the ooze at the bottom. Water plants may be crowded into a glass dish and allowed to decay, and after about two weeks the amœba may be found in the brown slime scraped from the plants. An amœba culture sometimes lasts only three days. The most abundant supply ever used by the writer was from a bottle of water where some oats were germinating. Use ⅕ or ⅙ inch objective, and cover with a thin cover glass. Teachers who object to the use of the compound microscope in a first course should require a most careful study of the figures. [Illustration: FIG. 9.—AMŒBA PROTEUS, much enlarged. ] [Illustration: FIG. 10.—AMŒBA. _cv_, contractile vacuole; _ec_, ectoplasm; _en_, endoplasm; _n_, nucleus; _ps_, pseudopod; _ps_, pseudopod forming; ectoplasm protrudes and endoplasm flows into it. ]