The arrangement of the tangential tubes, which originally, in the simplest Aulosphærida, lie tangentially in the spherical face of a simple lattice-sphere, exhibits various secondary modifications, leading to various interesting generic forms. Two genera only, Aularia (with triangular meshes, Pl. [111], fig. 2) and Aulonia (with polygonal meshes, Pl. [111], fig. 1) possess a smooth, perfectly simple lattice-sphere, and may therefore be regarded as the ancestral genera of the two subfamilies. Two other corresponding genera, the common Aulosphæra (Pl. [109]) and the rarer Aulastrum (Pl. [111], fig. 3), differ from the former in the development of radial spines at the nodal points of the simple lattice-sphere. Aulophacus may be developed from Aulosphæra by shortening, Aulatractus, however, by prolongation of the vertical main axis (Pl. [111], figs. 6, 7). In two genera, Auloplegma and Aulodictyum, the latticed wall of the spherical shell becomes thickened and spongy, an irregular framework being formed by tubes connected in different directions (Pl. [111], fig. 8). The most remarkable and the most elegant form, however, of the whole family is represented by Auloscena (Pl. [110]). The entire surface of the spherical lattice-shell is here covered with numerous regular or subregular pyramids, or tent-shaped elevations. Usually each pyramid is six-sided, and surrounded by six other six-sided pyramids, their bases being separated by six triangular meshes, which lie in the spherical face. A similar elegant form is developed among the Sagosphærida in the genera Sagoscena, Sagenoscena and Sagoplegma (Pl. [108], fig. 1). The structure of Auloscena, however, is usually more regular, and in the top of each pyramid a radial tube arises.
The junction of the cylindrical tubes at the nodal points of the network is very remarkable. Aularia, the simplest form of the family, exhibits at each nodal point the union of six tangential tubes (Pl. [111], fig. 2); their ends are so pointed and truncated that they are connected in the form of a regular six-radiate star; the conical end of each tube is separated from, and at the same time closely connected with, the adjacent conical ends of the two neighbouring tubes by a thin septum, the astral or sutural septum. The six astral septa compose together a six-radiate star, and in the centre of this star the six axial filaments of the tubes are united. Their central union is surrounded by a small, double-contoured circle, and this circle seems to be the perimeter of a small and flat cavity on the inside of the star, which we call shortly the "nodal cavity" ("die kleine Vertiefung" according to Hertwig, loc. cit., p. 90). The nodal cavity of Aularia probably possesses a central opening on its inside and six small surrounding pores, which lead into the six connected tangential tubes. In Aulosphæra and Auloscena, where a radial spine arises at each nodal point, its axial filament arises from the centre of the star, and is usually prolonged on the inside into a free centripetal beam (Pl. [109], figs. 6, 7; Pl. [110], figs. 4, 6). This centripetal beam is a slender, very thin, conical tube (often with a six-sided pyramidal base) and perhaps of great morphological interest as a rudiment, being homologous to the hollow radial beams which connect the two concentric spheres of the Cannosphærida. Possibly the Aulosphærida have been derived from the latter by loss of the inner shell and reduction of the radial beams; the centripetal beams which are found in many (but not in all) Aulosphærida, may be the last remnant of those radial beams. They contain also an axial filament, as a direct internal prolongation of that of the external radial spine. The axial filaments of the radial spines are usually connected with their thin wall by a variable number of scattered transverse threads, or sometimes even by thin transverse septa (Pl. [110], figs. 4-7, &c.). This structure corresponds to the similar axial filaments and their thin filiform transverse branches which we have found in other Phæodaria, e.g., in the Tuscarorida and Circoporida.
The Aulonida (with polygonal meshes) exhibit in general the same structure as the Aularida (with triangular meshes). But whilst in the latter usually six tangential tubes are united at each nodal point, in the former only three or four tubes become united. Therefore also the number of the small sutural partitions or astral septa, which radiate from the central openings of the nodal cavity, is six in the latter, three or four in the former. Correspondingly three or four small pores lead from the nodal cavity into the surrounding tangential tubes.
The true nature of the nodal points, and the intimate structure of the different parts here united, is a matter which it is very difficult to explain. It is a certain fact, well established by hundreds of observations, that in the complete and well-preserved skeletons which are perfectly purified by fire, or by hot mineral acids, and afterwards dried, all the tubes of the skeleton, the tangential as well as the radial cylinders, become filled up by air. Each tube contains usually one large cylindrical air-bubble, with two hemispherical ends. But the air-bubbles of the neighbouring tubes are completely separated one from another by the thin astral or sutural septa, and the air-bubble of the radial tubes is also separated from the former. The central cavity of each nodal point is therefore surrounded in the Aularida by six, in the Aulonida by three or four separate cylinders of air. This fact seems to be explained only on the supposition that each single tube has two terminal pores or fissures, which open into the two nodal cavities on its two ends. The radial tubes must also possess at least one small opening, probably on their base, and probably they have another on their distal apex. In no other way can it be explained, that in all complete, well-preserved and purified skeletons, each single tube constantly becomes easily filled by an air-bubble after drying.
In the living Aulosphærida the cavities of all tubes are filled up by a jelly-substance, which may be stained by carmine and is probably identical with the jelly of the calymma. The latter is probably in direct connection with the former by the central pore of the nodal cavity, which is placed on its inside and surrounded by the astral septa; these separate the tangential tubes, radiating from one nodal point, completely, and are thin and simple, but very solid lamellæ of silica. Therefore the nodal stars of broken shells usually remain united, whilst the single radiating tubes composing them are broken off (Pl. [110], figs. 3, 8, 10). But it happens only rarely (and only in certain individual species) that complete single tubes separate; usually the fragments of the connected neighbouring tubes remain on their ends. The two small terminal openings of each tangential tube, which lead from its cavity into the nodal cavity, and are surrounded on each end by the truncated ends of two neighbouring astral septa, are very difficult to observe (Pl. [110], figs. 8-10).
The wonderful elegance and the high complication of these regular skeletons of the Aulosphærida, produced by a single cell, becomes increased by the graceful and manifold appendages and apophyses which are usually developed on the radial tubes. In only a few species these are simple, as in the common and cosmopolitan Aulosphæra trigonopa. Usually lateral or terminal appendages are developed in great variety, a selection of which is figured in Pls. [109]-[111]. The lateral branches are either irregularly scattered spines (Pl. [110], figs. 3-7) or regular verticils of cruciate or radiate spines; each verticil is usually composed of four perpendicularly crossed horizontal branches (Pl. [109], figs. 3, 4, 7, 10, &c.), more rarely of a greater number of radiating transverse branches.
The terminal appendages of the radial spines exhibit a striking similarity with those of the Aulacanthida (Pls. [102]-[105]). They are either forks with two or three divergent branches (Pl. [111], figs. 3, 4), or regular crosses with four branches opposite in pairs (Pl. [109], figs. 2, 6, 7, 10), or elegant crowns or verticils, composed of numerous radiating branches (Pl. [110], figs. 1-6). The distal ends of the terminal as well as of the lateral branches are either simple, pointed, or armed with a spinulate knob, or with a terminal spathilla. The variety and elegance of these terminal ornaments, the function of which is that of capturing tentacles, is in the Aulosphærida not less admirable than in the Aulacanthida and Cœlodendrida.
The central capsule of the Aulosphærida (Pl. [111], fig. 2) was first figured in my Monograph (1862, Taf. xi. fig. 5) of Aulosphæra elegantissima, as a sphere of 0.2 to 0.3 mm. in diameter. I described there the large nucleus (of half that size) as a spherical "Binnenblase," and the numerous pseudopodia which arise from the capsule and radiate through the meshes of the lattice-shell. But I had not observed at that time the three typical openings of the capsule, which were first discovered and accurately described by R. Hertwig (1879, loc. cit., p. 94, Taf. x. figs. 2, 4, 5, 8, 14). The large astropyle with its radiate operculum and proboscis, and the two smaller lateral parapylæ, provided with a smaller tubule, have in general the same shape as in the closely allied Sagosphærida and Orosphærida, and agree in their strong development with that of the Aulacanthida. The collection of the Challenger contains numerous well-preserved preparations of Aulosphærida, which were stained by carmine immediately after being captured, and in which the central capsule and its nucleus exhibit the same intimate structure already accurately described by R. Hertwig. The diameter of the capsule is usually between 0.2 and 0.3, rarely less than 0.15 or more than 0.35 mm., the nucleus has half that size. The phæodium has usually about the same volume (Pl. [109], fig. 1), but seems to be in many Aulosphærida less developed than in the other Phæodaria.
Synopsis of the Genera of Aulosphærida.
I. Subfamily Aularida. Meshes of the network triangular, regular or subregular. Six tangential tubes united at each nodal point of the net. |  | Shell spherical, with a simple network. |  | Without radial tubes, | 682. Aularia. |
| With radial tubes in the nodes of the net, | 683. Aulosphæra. | ||||
| Shell spherical, with pyramidal elevations or with spongy framework. |  | Shell covered with pyramidal elevations, the top of which bears a radial tube, | 684. Auloscena. | ||
| Shell with spongy framework, the surface of which bears radial tubes, | 685. Auloplegma. | ||||
| Shell not spherical, either lenticular or spindle-shaped, with simple network. |  | Shell lenticular, with shortened main axis and radial tubes, | 686. Aulophacus. | ||
| Shell spindle-shaped, with prolonged main axis and radial tubes, | 687. Aulatractus. | ||||
II. Subfamily Aulonida. Meshes of the network polygonal, usually irregular. Three or four (rarely more) tangential tubes united at each nodal point. | | Shell spherical, with a simple network. | | Without radial tubes, | 688. Aulonia. |
| With radial tubes in the nodes of the net, | 689. Aulastrum. | ||||
| Shell spherical, with a spongy framework. | Without radial tubes, | 690. Aulodictyum. |