The "rhinocanna or nasal tube" (Pl. [126], figs. 1, 4; Pl. [127], figs. 4-9t) is a very remarkable organ which is common to all Cœlographida (without any exception), and distinguishes them markedly from all the other Radiolaria, and particularly from the closely allied Cœlodendrida in which we find no trace of it. The rhinocanna is a cylindrical or three-sided prismatic hollow tube, which lies in the sagittal plane, on the outer surface of each valve, arises from the base of the galea, and is directed towards the proboscis of the central capsule. The two opposite rhinocannæ open on each side of the latter (Pl. [127], figs. 4-9m), and usually this "nasal mouth" or the anterior opening of the nose is somewhat dilated or even funnel-shaped. The posterior opening of the nose passes directly over into the base of the cavity of the galea.
Usually the rhinocanna is densely filled up by dark phæodella, which enter by this channel into the cavity of the galea (Pl. [127], figs. 4, 5, 9). Sometimes the entire phæodium is enclosed in the two galeæ and their rhinocannæ (figs. 5, 9), whilst at other times a great part of the phæodium lies outside of their cavities, and surrounds the proboscis of the mouth, or even the anterior half of the central capsule (fig. 4). The length of the cylindrical rhinocanna is usually about equal to that of the galea, whilst the diameter of the latter is from three to five times as great as that of the former. The structure of the thin wall is the same in both. The fine reticulation (fig. 8) is produced either by true, very small and irregular pores, or by a fine network placed on the solid thin wall. We may distinguish on each rhinocanna an outer or distal convex face, which is opposite to the proximal concave face of the galea, and an inner concave or proximal face, which rests immediately upon the convex outer face of the shell-valve; a thin solid lamella of silica here completely separates the cavities of the valve and of the rhinocanna resting upon it.
The "frenula or nasal suspensoria" (Pl. [127], figs. 4-9b) are thin ligaments of silica, which connect the nasal mouth (m) with the base of the main tubes arising from the galea; they are, therefore, also common to all Cœlographida, and an exclusive and marked attribute of this family. They are, however, different in the two subfamilies of this group, corresponding to the different origin of the odd or paired main tubes. In the Cœloplegmida (Pls. [126]-[128]) from the apex of each galea arises an odd main style, the nasal style (g 1), and its base is connected with the nasal mouth by an odd frenulum (b). In the Cœlotholida however (Pl. [122]) the large nasal odd style is always wanting, and there arise two paired frontal tubes from the two corners of the truncate frontal face of the galea; therefore two paired frenula are developed (a right and a left), and these, converging towards the nasal mouth, connect its distal corner with the base of the two frontal tubes.
The odd frenulum of each valve of the Cœloplegmida lies therefore in the sagittal plane, whilst the two paired frenula of the Cœlotholida lie on both sides of it, to the right and left. The frenula seem to be supporting columellæ or pillars, which support the fragile skeleton, and mainly effect a fixed prop for the fragile galea. In the Cœlotholida the frenula are often rather broad and irregularly fenestrated lamellæ of silica (Pl. [122], fig. 2), whilst in the Cœloplegmida they are usually thin ligaments, fenestrated only at the broadened ends, which are inserted inside on the distal apex of the nasal mouth, and outside on the base of the nasal main styles.
The large hollow tubes which arise from the galea of all Cœlographida, are very variable in number, size and shape, but are always richly branched and symmetrically arranged in the dorsal and the ventral valve of the shell. They exhibit an important difference in the two subfamilies of the group; in the Cœlotholida all the branches, and also the thin terminal ramules, are free, without any junction; in the Cœloplegmida, however, they communicate by frequent anastomoses, and the connected terminal ramules form on the surface of the calymma an outer lattice-mantle of very delicate network. Another marked difference between the two families is indicated by the origin and site of those main tubes which are connected with the rhinocanna by a frenulum. In the Cœloplegmida an odd, very large main tube (the nasal style) arises from the anterior apex of each galea and bears on its base an odd frenulum. This nasal style and its frenulum is altogether wanting in the Cœlotholida, where two paired main tubes (the frontal tubes) arise from the lateral corners of the truncate anterior side of the galea, and are connected with the mouth of the rhinocanna by two paired convergent lateral frenula.
We distinguish in all Cœlographida two different forms of hollow branched tubes, which we will call "brushes" and "styles." The brushes are dichotomously branched from the base, not verticillate; their distal ramules remain separate in the Cœlotholida and compose the spiny surface, of the peculiar "fork-thicket" whilst in the Cœlographida they become connected by frequent anastomoses and form the outer "lattice-mantle." The styles however are much longer projecting over the surface of the thicket or the mantle, and are not dichotomously branched, but verticillate, or armed with cruciate or alternately cruciate pairs of branches; the larger branches of the styles may be again dichotomously branched like the brushes; whilst the free prominent parts of the styles are always verticillate or cruciate-pinnate. The brushes are identical with the hollow tubes of the Cœlodendrida, whilst the styles are peculiar forms of apophyses, wanting in the latter.
The minimum number of hollow tubes which arise from each valve is three, and these are probably homologous with the three primary tubes of the Cœlodendrida. Two of these are paired (right and left), whilst the third is odd and lies in the sagittal plane; they have the same position as in the tripodal Nassellaria, and may therefore bear the same names, the two paired anterior or pectoral tubes being divergent forwards, the odd or caudal tube being bisected backwards (so in the Cœlotholida, Pl. [121]). The odd caudal tube (probably identical with the odd tube of the Cœlodendrida) is always a brush, dichotomously branched, and never prolonged into free style. The two paired frontal or pectoral tubes, however are usually prolonged into two long verticillate styles. The basal origin also of these three primary tubes is different. The two pectoral or anterior paired tubes always arise from the galea itself whilst the posterior odd or caudal tube usually arises behind the galea from the valve (Pl. [127], figs. 4-8, g 6).
Since these three primary tubes the odd caudal and the paired pectoral, are probably homologous in all Cœlographida and Cœlodendrida, they have a great morphological importance, similar to the three primary feet of the Nassellaria. All other tubes arising from the valves must be regarded as secondary apophyses, since they are not constant in all members of the two families, but present only in some of them. All the Cœlotholida observed (a small number of species only) possess no secondary tubes, but only the three primary; whilst all Cœloplegmida possess one or more secondary tubes, and one of these is constant, viz., the odd nasal style, directed towards the mouth, and arising as the foremost from the apex of the galea (Pl. [127], figs. 4-8, g 1).
The maximum number of tubes observed, which arise from each valve in the Cœloplegmida, is eleven; five of these are odd and placed in the sagittal plane of the body, viz.:—(A) the primary caudal tube (Pl. [127], figs. 4-8, g 6); (B) an odd procaudal tube, arising between the caudal and the sagittal tube; (C) the sagittal tube, placed either in the sagittal axis of the body or near it (often prolonged into a sagittal style, Pl. [128], fig. 1); (D) an odd postnasal tube, arising between the sagittal and the nasal tube; (E) the odd nasal tube, constant in all Cœloplegmida, and connected at its base by the odd frenulum with the rhinocanna (Pl. [127], figs. 4-8, g 1). All other tubes occurring in the Cœloplegmida are paired, and symmetrically arranged on both sides of the sagittal plane, at right and left; their maximum number is three pairs, viz.:—(F) the paired pectoral tubes (as the foremost), directed forwards; (G) the paired frontal or lateral tubes, placed either in the frontal axis of the valve, or in a neighbouring axis, directed towards the right and left pole (Pl. [127], figs. 4-8, g 4 and g 5); (H) the paired tergal tubes, directed backwards (constant in all Cœloplegmida). The origin of these tubes is rather variable, since they arise in nearly allied species, sometimes independently of one another, at other times united at the base. But a closer comparison of them in the different species will demonstrate their homology, caused by constant heredity.
The terminal ramules of the brushes, which form the subspherical "fork-thicket" in the Cœlotholida, the outer "lattice-mantle" in the Cœloplegmida, are constantly armed at the distal ends either with spathillæ or with anchor-pencils, bunches of those most elegant spinulate threads, which bear at the free end an anchor, or a whorl of two, three, or four recurved teeth (Pl. [122], fig. 8; Pl. [127], fig. 10; Pl. [128], figs. 1, 6). The pencils are usually dichotomously branched, their threads zig-zag or delicately serrate, often armed with very small recurved denticles, and the anchor teeth (commonly three or four) are usually smooth on the convex outer, serrate on the concave inner edge. The entire surface of the subspherical thicket in the Cœlotholida, and of the polyhedral lattice-mantle in the Cœloplegmida, is armed with thousands of those most elegant spathillæ, or anchor-pencils.