The _Foraminifera_ (perforated animals), of this class, have several peculiarities. The body is even more simple, being apparently without layers or cavity. The processes thrown out as arms and legs are not blunt or massive, but long and slender. And, moreover, small as it is, it has the wonderful property of secreting about itself an envelope, whose thin walls are built of the carbonate of lime. The delicate little structures are often singularly beautiful. Some are monads, having but a single shell; others, by a process of budding add new cells or chambers, often in a spiral coil. These are marine shells, and their numbers in many parts of the ocean are astounding. The bottom of the sea, for many degrees on both sides of the equator, wherever examined by dredging, is found covered with them, either still in their organic state, or ground by attrition to a fine lime dust. It is estimated that a single pound of the sea bottom in some localities contains millions of them, and they are the principal material of the chalk hills. CLASS IV.—_Infusoria._ This class includes _Vorticella_ (wheel animals), _Flagellata_ (whip-shaped animals), _Tentaculata_ (having tentacles), and others. Their general characteristics do not differ widely from those already mentioned. As the name imports, they are mostly found in vegetable infusions that have been exposed for some time, and are directly the product of invisible cells or animal germs that were floating in the atmosphere till a lodgment was found favorable to their development. Those called _Vorticella_, to the eye seem simply mould on the plant to which they are attached, but under the glass their animal qualities appear; and they multiply with amazing rapidity. Every drop of water from a stagnant pool is full of these animalculæ, of various shapes and dimensions, some of them constantly in motion, propelled by numerous cilia, or slender, hair-like appendages that fringe the circumference, and are used as oars. Their whole organism, though delicate, and having a thin membranous covering, is imperfect. There are two contractile openings, with a slight depression at the mouth, leading to a funnel-shaped throat, into which the nutritive substances descend. SUB-KINGDOM II.