146. _The Ontogeny of the Spumellaria._--In the simplest case the individual development in the SPUMELLARIA ceases with the _Actissa_-stage. In all other genera of this legion diverging forms proceed from this, of which the different growth of the three dimensive { xcvi}axes on the one hand (§§ 44, 45), and the differentiation of the various parts of the unicellular organism with the formation of the skeleton on the other, are of pre-eminent significance. Even in the varying growth of the central capsule in the different dimensions of space in the skeletonless #Colloidea#, four different modes may be distinguished, which further, in the corresponding development of the skeleton, furnish the basis for the origin of the four orders of #Sphærellaria#. The most primitive and simplest form of growth, equal extension in all directions, is found in the spherical central capsule and the concentric spherical skeletons (_Procyttarium_, #Sphæroidea#). When the growth of the central capsule proceeds more rapidly in the direction of the vertical main axis than in any other direction, the ellipsoidal or cylindrical central capsule (_Actiprunum_) arises, and the vertically elongated skeleton of the #Prunoidea#, which is derived from it. When, on the contrary, the growth of the central capsule and lattice-shell is less in the direction of the vertical main axis than in any other direction, the lenticular or discoid central capsule (_Actidiscus_) arises, and the corresponding lenticular shell of the #Discoidea#. Finally, even quite early in many SPUMELLARIA, the growth of the central capsule and of the corresponding lattice-shell in the three dimensive axes is different, and hence arise the lentelliptical forms whose geometrical type is the triaxial ellipsoid or the rhombic octahedron (_Actilarcus_, #Larcoidea#). Thus the origin of the four orders of #Sphærellaria# is simply explained by a varying growth in the different dimensive axes. The _primary_ (innermost) lattice-shell is in this legion always _simultaneously_ developed (suddenly excreted at the moment of lorication from the sarcodictyum). The _secondary_ lattice-shells, on the other hand, which surround the former concentrically, and are united with it by radial bars, arise _successively_ from within outwards.