131. _Dictyosis of the Spumellaria._--Siliceous lattice-structures are wanting in the first section of the SPUMELLARIA, the #Collodaria#, but in the second section, #Sphærellaria#, they are developed in extraordinary variety of details. In spite of this extreme richness in different forms, the lattice-shells of the SPUMELLARIA may all be derived from one and the same primitive ground-form, a simple lattice-sphere with regular hexagonal meshes (_Phormosphæra_, p. 61, Pl. 12, figs. 9-11; _Heliosphæra_, &c.). {lxxxvii}The siliceous bars which bound these regular and subregular meshes are at first exceedingly then and filiform; afterwards they become thicker or spread out laterally, whence the meshes often become round with a hexagonal frame (Pl. 12, fig. 5; Pl. 28, fig. 1). If the latter vanish, a lattice-shell with simple circular meshes is formed. Very commonly the regular form of the meshes or pores becomes more or less irregular, polygonal, or roundish. Hence, in general, four different principal forms of dictyosis may be distinguished among the SPUMELLARIA; viz. (1) regular or subregular _hexagonal_ meshes; (2) regular or subregular _circular_ meshes; (3) irregular _polygonal_ meshes; (4) irregular _roundish_ meshes. The three latter forms are to be regarded as secondary, derived from the primary first form. In those SPUMELLARIA which possess several concentric lattice-shells enclosed one within another, either these have all the same form of dictyosis, or the lattice-work of the innermost primary shell is different from that of the outer secondary shells (Pls. 19, 20); sometimes these latter also differ more or less among themselves (§ 129).