Page:EB1911 - Volume 22.djvu/821

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804
RADIOLARIA


disposed on five successive zones of four on alternating meridians, the zones corresponding to equator, tropics and circumpolar circles on the globe; pores of central capsule in scattered groups.

Fam. 1. Actinelida. Spines numerous, more than twenty, irregularly grouped. Litholophus, Haeck.; Xiphacantha, Haeck.

Fam. 2. Acanthonida. Spines twenty, simple, usually equal. Acanthometra, J. Müll. (fig. iv. 6, 7); Astrolonche, Haeck.; Amphilonche, Haeck. (fig. III. 18).

Fam. 3. Sphaerophractida: Spines equal, branching and often coalescing into a latticed shell, homaxonic.

Fam. 4. Prunophractida: Branching spines coalescing into a latticed shell which is elongated and elliptical in at least one plane.

C. Nassellaria, Haeck. (Monopylaea, Hertw.). Silico-skeletal Radiolaria in which the central capsule is typically monaxonic (cone shaped), with a single perforate area (pore-plate) placed on the basal face of the cone; the membrane of the capsule, the nucleus single; the skeleton is extracapsular, and forms a scaffold-like or beehive-like structure of monaxonic form, a tripod or calthrop, a sagittal ring, or a combination of these.

Fam. 1. Nassoidea, Haeck. Skeleton absent. Cystidium, Haeck.

Fam. 2. Plectida, Haeck. Skeleton formed of a single branching spicule, a tripod or usually a 4-radiate calthrop, its branches sometimes reticulated. Genera: Plagiacantha, Haeck.; Plegmatium, Haeck.

Fam. 3. Spyroidea. Shell latticed around the sagittal ring (“cephalis”), sometimes with a lower chamber added.

Fam. 4. Botridea, Haeck. Shell latticed, composed of several chambers agglomerated without definite order; a single central capsule. Genera: Botryocyrtis, Haeck.; Lithobotrys, Haeck.

Fam. 5. Cyrtoidea, Haeck. Skeleton a monaxonic or triradiate shell, or continuous piece (beehive-shaped). Genera: Halicalyptra, Haeck.; Eucyrtidium, Haeck. (fig. II.); Carpocanium, Haeck. (fig. IV. 3).

Fam. 6. Stephoidea, Haeck. Skeleton a sagittal ring continuous with the branched spicule, and sometimes growing out into other rings or branches. Genera: Acanthodesmia, Haeck.; Zygostephanus, Haeck.; Lithocircus, Haeck. (fig. IV. 1).

D. Phaeodaria, Haeck. (Tripylaea, Hertw.). Radiolaria of cruciate symmetry, prolonged into tubular processes with three oscula to the central capsue, one inferior, the principal, and two symmetrically placed on either side of the opposite pole; skeleton of spicules, a network of hollow filaments, or a minutely alveolate shell, of a combination of silica with organic substance; extracapsular protoplasm containing in front of the large oscule an agglomeration of dusky purplish or greenish pigment (“phaeodium”).

Fam. 1. Phaeocystida, Haeck. Siliceous skeleton absent or of separate needles. Genera: Aulacantha, Haeck.; Thalassoplancta, Haeck.

Fam. 2. Phaeosphaerida. Spicules united into a latticed shell. Genera: Aulosphaera, Haeck. (fig. IV. 9); Auloplegma, Haeck.; Cannacantha, Haeck.

Fam. 3. Phaeogromida, Haeck. Shell continuous, traversed by fine canals or finely alveolate, provided with at least one pylome. Genera: Challengeria, Wyv., Thomson; Lithogromia, Haeck.

Fam. 4. Phaeoconchida. Shell as in Phaeosphaerida, but of two symmetrical halves (valves), which meet in the plane of the three oscules (“frontal” of Haeckel, who terms the plane of symmetry through the shells “sagittal”). Genera: Conchidium, Haeck.; Coelodendrum, Haeck. (fig. IV. 4).

The following passages may be repeated here from Sir E. Ray Lankester's article “Protozoa” in the 9th edition of this Encyclopaedia:—

“The important differences in the structure of the central capsule of different Radiolaria were first shown by Hertwig, who also discovered that the spines of the Acanthometridea consist not of silica but of an organic compound (but see above). In view of this latter fact and of the peculiar numerical and architectural features of the Acanthometrid skeleton, it seems proper to separate them altogether from the other Radiolaria. The Peripylaea maybe regarded as the starting-point of the Radiolarian pedigree, and have given rise on the one hand to the Acanthometridea, which


EB1911 Radiolaria (1).jpg

Fig. III.-Radiolaria. 1. Central capsule of Thalassicolla nucleata, Huxley, in radial section. a, the large nucleus (Binnenbläschen); b, corpuscular structures of the intracapsular protoplasm containing concretions; c, wall of the capsule (membranous shell), showing the fine radial pore-canals; d, nucleolar fibres (chromatin substance) of the nucleus. 2, 3. Collozoum inerme, J. Müller, two different forms of colonies, of the natural size. 4. Central capsule from a colony of Collozoum inerme, showing the intracapsular protoplasm and nucleus, broken up into a number of spores, the germs of swarm-spores or flagellulae; each encloses a crystalline rod. c, yellow cells lying in the extracapsular protoplasm. 5. A small colony of Collozoum inerme, magnified 25 diameters. a, alveoli (vacuoles) of the extracapsular protoplasm; b, central capsules, each containing besides protoplasm a large oil-globule. 6-13. Yellow cells of various Radiolaria: 6, normal yellow cell; 7. 8, division with formation of transverse septum; 9, a modified condition according to Brandt; 10, division of a yellow cell into four; 11, amoeboid condition of a yellow cell from the body of a dead Sphaerozoon; 12, a similar cell in process of division; 13, a yellow cell the protoplasm of which is creeping out of its cellulose envelope. 14. Heliosphaera inermis, Haeck., living example; a, nucleus; b, central capsule; c, siliceous basket-work skeleton. 15. Two swarm-spores (flagellulae) of Collozoum inerme, set free