elsewhere than from the stylopodium, in the whole of the "Vitrea" and in many "Arenacea"; and, as we shall see, this may exercise a marked influence on the structure of the shell. In some cases the shell is simple, and in _Cornuspira_ and _Spirillina_ increases so as to have the form of a flat coiled tube. In _Calcituba_ the shell branches irregularly in a dichotomous way, and the older parts break away as the seaweed on which they grow is eaten away, and fall to the bottom, while the younger branches go on growing and branching. The fallen pieces, if they light on living weed, attach themselves thereto and repeat the original growth; if not, the protoplasm crawls out and finds a fresh weed and forms a new tube. In the "Polythalamia" new chambers are formed by the excess of the protoplasm emerging and surrounding itself with a shell, organically united with the existing chamber or chambers, and in a space-relation which follows definite laws characteristic of the species or of its stage of growth, so as to give rise to circular, spiral, or irregular complexes (see Fig. 13). {65}[Illustration: FIG. 14.—Various forms of _Foraminifera_. In 4, _Miliola_, _a_, shows the living animal; _b_, the same killed and stained; _a_, aperture of shell; _f_, food particles; _nu_, nucleus; _sh_, shell. (From Parker and Haswell, after other authors.)] In most {66}cases the part of the previously existing chamber next the pylome serves as the hinder part of the new chamber, and the old pylome becomes the pore of communication. But in some of the "Perforata" each new chamber forms a complete wall of its own ("proper wall," Fig. 13, 8_b_), and the space between the two adjacent walls is filled with an intermediate layer traversed by canals communicating with the cavities of the chambers ("intermediate skeleton"), while an external layer of the same character may form a continuous covering. The shell of the Perforata may be adorned with pittings or fine spines, which serve to increase the surface of support in such floating forms as _Globigerina_, _Hastigerina_, and the like (Fig. 17). In the "Imperforata" the outer layer is often ornamented with regular patterns of pits, prominences, etc., which are probably formed by a thin reflected external layer of protoplasm. In some of the "Arenacea" a "labyrinthine" complex of laminae is formed.