The parapylae are perforations symmetrically placed near the main axis of the capsule, but at the opposite end to the astropyle. Two are commonly present, rarely one three, six, or more (Circoporida, Tuscarorida). A parapyla consists of a small ring or short tube, from which springs a conical or cylindrical tubule, the paraboscis.
1The innermost or two innermost shells, termed medullary, differ sometimes in the character of their lattice-work from the outer or cortical shells. See Haeckel, op. cit. supra, pp. lxxxv-vi.
The intra-capsular protoplasm is finely granular; a radial striation is observable in many Spumellaria, which becomes masked by the formation of vacuoles, etc.; the peripheral zone may be broken up into radial granular wedges, separated by clear intervals. In the Nassellaria a portion of it undergoes differentiation as the podocone, a conical mass with its base resting on the porochora and traversed by striae from base to apex. It is more resistent to reagents and stains more deeply, especially at its apex, than the rest of the protoplasm1. In the large Phaeodaria the peripheral zone of protoplasm is fibrillated, the fibrils, which are perhaps of a muscular nature, running meridionally from one pole of the capsule to the other and radiating towards the capsular apertures, beneath which only they are sometimes visible. The protoplasm contains vacuoles, oil-globules, pigment, crystalloids, concretions, and the nucleus. Vacuoles, or hyaline spheres, are, except in Nassellaria, commonly present, sometimes in great numbers and of so large a size as to become polyhedral through mutual pressure (some Thalassicollidd). They are hyaline, their contents a saline fluid or gelatinous sphere, the jelly apparently of similar character to the extracapsular (infra), or a coagulable albumen (some Thalassicollida)2. Fatty granules are universally present.
Oil-globules are very general in Spu-mellaria and Nassellaria, rare in Acantharia, absent as a rule in Phaeodaria. There is one, central and large in most colonial species, but in other cases there are several globules for the most part numerous and peripheral. They are highly refractile, usually colourless, but may be yellow, brown, red, blue; and in the Spumellaria, especially the colonial, with a laminated organic substratum, not albuminous according to Brandt. Pigment, red, yellow, brown, rarely violet or blue, still more rarely green, is present as minute granules. Crystalloids, usually known as crystals, are of two kinds (1) small, more or less like a whetstone, destined to be inclosed as reserve material one in each spore, not observed in Nassellaria or Phaeodaria;
(2) large, apparently of an excretory nature, and indestructible by a red heat, present only in some colonial Collosphaerida, side by side with the small. Both kinds are formed only when sporulation is about to take place, as is the blue pigment of Collosphaera Huxleyi and Myxosphaera coeridea. Masses of crystals (? excretory) occur in the vacuoles of Thalassi-collida and some Phaeodaria. Laminated circular or elliptical concretions of unknown nature are found in some Spumellaria and Nassellaria; violin-shaped and highly refractile bodies in the same two groups and some Acantharia. The nucleus is at first single, but in the colonial Spumellaria and very many Acantharia, it undergoes division into many nuclei at an early period. The single nucleus is central and often of large size, e. g. 1-2 mm. in some large Thalassicollida; in most Phaeodaria it attains -2/3 - 3/4 of the diameter of the central capsule. Its shape is typically spherical, but varies concomitantly with that of the capsule; it is sometimes irregular and occasionally has radial claviform processes (Thalassophysay Thalassophila). It may inclose by growth one or more of the inner shells when the shell is multiple. The small nuclei of the colonial Spumellaria are homogeneous, but in the Acantharia they may be nucleolate.
The single nucleus has a distinct membrane, thick, double contoured, and in Thalassicollida probably porous. It is more or less homogeneous, and may possess nucleoli (some Spumellaria, the Nassellaria and Phaeodaria). A chromatin network with nucleolar enlargements has been demonstrated in Thalassicolla coeridea.
1The porochora of the central capsule contains vertical rods which stain deeply. They are perforated according to Hertwig, solid according to Haeckel and Biitschli. The striae of the podocone correspond to these rods; they are tubular (Hertwig), or perhaps contractile, i. e. muscular, threads (Haeckel).
3Haeckel regards the vacuoles as belonging to two categories, (I) true vacuoles which are droplets in the protoplasm, and (2) alveoles with a special but thin enveloping membrane. It is perhaps doubtful if the latter exist. An extreme stage of vacuolation is seen in Acanthometra elastica, where the protoplasm is reduced to a thin superficial reticulation, connected by threads to a central portion surrounding the spines.
The extracapsular portion of the body consists of a gelatinous skeleton or calymna, and protoplasm with various inclosures. It has been shown experimentally on Thalassicolla nucleata that it can be regenerated from the central capsule if the latter be removed artificially. The calymna is separated from the central capsule by the sarcomatrix (infra). It is hyaline, rarely opalescent, of the same degree of refrangibility as sea-water, structureless but occasionally laminated, of a soft consistence in the young . form, but varying in the adult, where it is sometimes as firm as cartilage. It grows during life, and is greatly developed in the Spumellarian Collo-daria. It resembles the skeleton in shape, and in Nassellaria and Phaeodaria usually incloses it completely. In the Acantharia a regularly polygonal network of fibres is disposed superficially between the calymnal sheaths of the spines. The protoplasm forms a layer or sarcomatrix immediately surrounding the central capsule; it is massed over the single aperture of the Nassellaria and the astropyle of Phaeodaria 1. From this layer a more or less irregular network of protoplasmic threads, the sarco-plegma, radiates to the surface of the jelly, where it forms a superficial network, the sarcodictyum, from which originate the pseudopodia.