127. _The Cannoid Skeleton._--Cannoid or tubular skeletons are those which are composed of hollow tubes; they occur exclusively in the PHÆODARIA or CANNOPYLEA. Tubular processes, nevertheless, occur in some other Radiolaria, as, for example, among the SPUMELLARIA in a portion of the Collosphærida (_Siphonosphæra_, _Caminosphæra_, Pls. 6, 7), and of the #Prunoidea# (_Pipetta_, _Cannartus_, &c., Pl. 39, figs. 6-10, &c.), also among the NASSELLARIA in _Theosyringium_ (Pl. 68, figs. 4-6), _Cannobotrys_ (Pl. 96, figs. 3, 4, 8-11, 20-22), &c. In all these cases, however, the tubes are direct processes of the cavity of the shell, the trabeculæ of the lattice-work being solid. Only in the CANNOPYLEA are the lattice-bars themselves, the radial spines and appendicular organs, generally tubular (hence the designation "Pansolenia"). The lumen of the thin-walled siliceous tubes is filled with jelly, and hence the specific gravity of the relatively large skeleton is considerably diminished. This peculiarity is not found in all CANNOPYLEA; it is wanting in all Sagosphærida and Concharida, as well as in a part of the Orosphærida and Castanellida; in the latter there are found intermediate stages between hollow and solid skeletal rods. Very often a fine siliceous thread runs in the axis of the tubes, which is connected with its wall by lateral branches (Pl. 110, figs. 4, 6; Pl. 115, figs. 6, 7). More seldom the tubes are divided by horizontal septa into a series of chambers (Medusettida, Pls. 118-120). The two families Aulosphærida (Pls. 109-111) and Cannosphærida (Pl. 112) are distinguished from all other PHÆODARIA by the fact that their tubes are separated by astral septa in the nodal points of the lattice-shell (§§ 112, 134).