_The Pseudopodia_ or the very fine, long, thread-like filaments of exoplasm arise in all Radiolaria in very great numbers from the surface of the matrix, and exhibit in general the same characteristic shape as in the other Rhizopoda. Their inner or proximal part is enclosed within the jelly-veil or calymma, whilst their outer or distal part floats freely in the sea-water. Their special motions and modifications exhibit considerable variations in different groups, their tendency to ramify, anastomose, and form networks being in some cases very small, in others very great. Also the characteristic motion of granules in the pseudopodia is very different. In general those most important exoplasmatic filaments serve as organs both for the vegetative functions of nutrition, and for the animal functions of motion and sensation. _The class_ Radiolaria can be divided according to its varying structure into four different legions or subclasses, the characters of which are the following:-- I. PERIPYLEA OR SPUMELLARIA. Membrane of the central capsule simple, perforated by innumerable very fine pores. Fundamental form originally homaxon or spherical. Skeleton wanting or siliceous. No phæodium in the extracapsular calymma. The Peripylea comprise two orders:-- A. COLLODARIA (without lattice-shell). B. SPHÆRELLARIA (with lattice-shell). II. ACTIPYLEA OR ACANTHARIA. Membrane of the central capsule simple, perforated by innumerable fine pores. Fundamental form originally homaxon or spherical. Skeleton acanthinic (not siliceous). No phæodium in the extracapsular calymma. The Actipylea consist of two orders:-- A. ACANTHOMETRA (without complete lattice-shell). B. ACANTHOPHRACTA (with complete lattice-shell). {5}III. MONOPYLEA OR NASSELLARIA. Membrane of the central capsule simple, perforated by a porous-area, or by one single large opening, divided into numerous very fine pores. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. No phæodium in the extracapsular calymma. The Monopylea comprise two orders:-- A. PLECTELLARIA (without complete lattice-shell). B. CYRTELLARIA (with complete lattice-shell). IV. CANNOPYLEA OR PHÆODARIA. Membrane of the central capsule double, perforated by one simple main-opening, prolonged into a tubulus, and besides this commonly by one or two (rarely more) small accessory openings. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. Constantly a peculiar dark pigment-body or "phæodium" in the extracapsular calymma. The Cannopylea comprise two orders:-- A. PHÆOCYSTINA (without lattice-shell). B. PHÆOCOSCINA (with lattice-shell). _Synopsis of the four Subclasses or Legions of Radiolaria._