Page:Scientific results HMS Challenger vol 18 part 1.djvu/216

8 all other Radiolaria—and are never aggregated in colonies; the calymma includes one single central capsule, and this again one central nucleus, which does not become divided until full maturity.

The on the contrary (or the Spumellaria socialia) live aggregated in large colonies; the calymma includes a variable number of associated central capsules and each of these commonly one central oil-globule, whilst the original simple nucleus commonly becomes very early divided into numerous small nuclei.

The Nucleus of the is originally constantly central, placed quite in the centre of the concentric capsule, and it retains this central position in all Monocyttaria or solitary Peripylea; whereas in the Polycyttaria—in consequence of its early division—its place is commonly taken by a central oil-globule. Whilst the numerous nuclei of the latter are very small, the single nucleus of the former is comparatively large, extremely large (more than a millimeter in diameter) in some gigantic.

The Endoplasm or the intracapsular sarcode exhibits in the greater number of a more or less distinct radial striation. It encloses a great variety of different parts; vacuoles, oil-globules, pigment-granules, crystals, &c.

The Membrane of the capsule in all is simple (never double as in the Phæodaria) and everywhere equally perforated by innumerable small pores; in the thick, double-edged membrane of many large  these pores appear (in the optical section of the capsule-wall) as distinct fine radial canals, very densely and regularly disposed.

The Central Capsule in the is originally a geometrical sphere, and this simple globular form is preserved in all, and in the greatest part of  and. By prolongation of one axis the form becomes ellipsoidal (or even cylindrical) in the, and in some few forms of. By shortening of one axis it becomes lenticular (or even discoidal) in the Discoidea, and in some few forms of. By unequal growth in three different axes, perpendicular one to another, the capsule becomes lentelliptical in all. Very rarely the capsule assumes in the a polyhedral or irregular (sometimes even amœboid) form, only in a few.

The Calymma, or the jelly-veil including the central capsule, is very voluminous in many of gigantic size, mainly in the large, and in all Polycyttaria or social Radiolaria. It includes here a considerable number of large vacuoles or "alveoli." The calymma never exhibits in this legion the dark voluminous phæodium, possessed by all.

Xanthellæ or "zooxanthellæ" are numerous in the calymma of most, but by no means constant; they are very variable in number and size.

The Matrix, placed between the calymma and central capsule, is, in the majority of the, a rather thick layer of granular exoplasm.

The Pseudopodia arising from it are very numerous, equally disposed over the whole