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TII

Online Encyclopedia
Originally appearing in Volume V10, Page 633 of the 1911 Encyclopedia Britannica.
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TII. AST RORHIZIDIACEAE.—Simple forms, rarely polythalamous (some Rhabdamminidae), but often branching or radiate; test arenaceous, loosely compacted and traversed by chinks for pseudopodia (Astrorhizidae), or dense, and opening by one or more terminal pylomes at ends of branches. Marine, Fam. The test of some Asirorhizidae is so loose that it falls to pieces when taken out of water. Haliphysenia is remarkable for its history in relation to the " gastraea theory." Pilulina has a neat globular shell of spongespicules and ' fine sand. Genera, Astrorhiza (Sandahl) in every case gives off granules and irregular masses. -(" chromidia ") of similar reactions, which play an important part in reproduction. During the maturation of the microsphere the nuelei.disappear; and the cytoplasm breaks up into, a large number of zoospores, each of which is soon provided with a single inns leua, whether. entirely derived from the parent-nucleus or front the coalescence 6fehromidia, or from both these sources is still uncertain... These zoospores are amoeboid ; they soon secrete a shell and reveal themselves as megalospheres, the original state of the megalospheric forms. In the adult megalosphere the solitary nucleus disappears and is re-placed by hosts of minute vesicular nuclei, formed by the.concentration of chromidia. Each nucleus aggregates around it a proper zone of dense protoplasm; by two successive mitotic divisions each mass becomes quadri-nucleate, and splits up into four biflagellate, uninucleate zoospores. These are pairing-cells of gametes, though they will not pair with members of the same brood. In the zygote resulting from pairing two nuclei soon fuse into one; but this again divides into two; an embryonic shell is secreted, and this Is the microspheric type, which is multinuclear from the first. F. Schaudinn compares the nuclei of the adult Foraminifera with the (vegetative) meganucleus of Infusora (q.v.) and the chromidial mass with the micronucleus, whose chief function is reproductive. Since megalospheric forms are by far the most abundant, it seems probable that under most conditions they also give rise to megalospheric young like themselves; and that the production of zoospores, (fig. 22), Pilulina (Carptr.) (fig. 19), Saccammin4 (Sars) (fig. 19), Rhabdammina (Sars), Botellina (Carptr.), Hallphysema (Bowerbank) (fig. 22). IV. LITUOLIDACEAE.—Shell arenaceous, usually fine-grained, definite and often polythalamic, recalling in structure calcareous forms. Lituola (Lamk.) (fig. 19), Endothyra (Phil.), Ammodiscus (Reuss), Loftusia (Brady), Hapl iphragmium (Reuss) (5g. 22), Thurammina (Brady) (fig. 22). V. MILIoLIDACEAB.—Shells porcellanous imperforate, almost invariably with a camptostyle leading from the embryonic (fig. 23, 3). IX. GLOBIGERINIDACEAE.—Shells vitreous, coarser perforated; chambers few spheroidal rapidly increasing in size; arranged in a trochoid or nautiloid spiral. Globigerina (I,amk.) (23, 6; 4, 12); Hastigerina (Wyville Thompson) (fig. 23, a); Orbulina (d'Orb,) (fig. 23, 8).
End of Article: TII
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TIIE SKULL FROM THE SIDE (norma lateralis)

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