The resemblance of the Foraminifera to the nautili and ammonites at first led naturalists to suppose that they formed part of the same class, which in a long course of centuries had dwindled down in less congenial seas to almost invisible dimensions; but a closer investigation proved them to belong to a much lower order of beings, nearly related to the Amœbæ, which likewise occur all over the ocean. Other animals excite our wonder by their complicated structure, but the amœba raises our astonishment by the excessive simplicity of its organisation. The amœba is nothing more than a living globule of mucus, a transparent, colourless, contractile substance, or plastic mass, the individual life of which shows itself in manifold changes of form, bearing the character of voluntary motion. When an amœba approaches another minute animal or plant unable to move out of its reach, it sends out extemporaneous feet, which soon clasp the prey on all sides, and the prisoner lies embedded in the living mucus until all his soluble parts have been absorbed. There is absolutely no trace of particular organs in the amœba; all its constituent particles may be used for any purpose, all equally move and digest, and each can at any time perform the organic functions pertaining to the whole. [Illustration: A Compound Foraminiferous Protozoon, magnified. The shell is perforated with holes, through which the different lobes of the animal communicate, and thread-like portions are protruded externally.] In their internal simplicity the Foraminifera are on a par with the amœbæ, and differ from them only in respect of their outward form. The amœbæ are naked, while the Foraminifera are covered with a shell, out of which, through one or numerous openings, the animal protrudes the processes which it requires for creeping or seizing its prey. These processes or filaments of mucus frequently ramify, closing as they spread, and sometimes covering an area of several lines in diameter, in the centre of which the animal inclosed in its shell waits for its prey, like a spider in its net. The extended filaments appear to have something venomous about them; for Dr. Schultze, to whom we owe an interesting monograph on the Foraminifera, frequently saw small and sprightly parameciæ, colpodes, and other infusoria drop down paralysed as soon as they touched the net. [Illustration: Various forms of Foraminifera. _a. Lagena striata._ _a′. Nodosaria rugosa._ _b. Marginulina raphanus._ _b′._ Longitudinal section of shell of ditto. _c. Polystomella crispa_, with its pseudopodia protruded. _d. Nummulites lenticularis_, shown in horizontal section. _e. Cassidulina lævigata._ _f. Textularia globulosa._ _g. Miliolina seminulum._ _g′._ Animal of Miliolina removed from its shell. ]