Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/872

Rh 848 PROTOZOA [RETICULARIA. Genera. Tinopciriis, Carpenter; Gitpsina, Carter; Aphroaina, Carter ; Thalamop&amp;lt;&amp;gt;ra t lioemer ; Polytretna, Kisso. [Sliell para sitic, encrusting, or arborescent ; surface areolated, coloured pink or white, Fig. XII. 9. Interior partly occupied by small chambers, arranged iu more or less regular layers, ami partly by non- spgmented canal-like spaces, often crowded with sponge-spicules No true canal system. This is one of the most important types as exhibiting the arborescent and encrusting form of growth. It is fairly abundant.] 2 * II 1 -~.* er f rata l - Spiral arrangement of simple chambers of a Reticularian shell. 2. Ditto, with double septal walls, and supple mental shell substance (shaded). 3. Diagram to show the mode in which successively-formed chambers may completely embrace their pre- 4. Diagram of a simple straight series of non-embracing 5. Ilaxtiyerina (Qlotrigerina) Murrayi, Wyv. Thomson a, bubbly (vacuolated) protoplasm, enclosing b, the perforated Globi- genna-like shell (conf. central capsule of Rad Solaria). From the peripheral protoplasm project, not only fine pseudopodia, but IK.HOW spines of calcareous matter, which are set ou the. shell, and have an axis of active protoplasm IMatric; drawn in the living state. C. Gl&amp;lt;&amp;gt;bi&amp;lt;jerina ulloide*, DOrb., showing the punctiform perforations of the shell and the main aperture. 7. Fragment of the shell of filobigerina, seen rom within, and highly magnified, a, fine perforations in the inner shell bstances ; 6, outer (secondary) shell substance. Two coarser perfora tions are seen in lection, and one lying among the smaller. 8 Or- Una unitena, D Orb. Pelagic example, with adherent radiating calcareous spines (hollow), and internally a small Globigerina shell. It is uncertain whether Orbulina is merely a developmental phase of Globi gerina. a, Orbulina shell ; b, (ilobigerina shell. 9. J olytreina ininia- ceuni, Lin.; x 12. Mediterranean. Example of a branched adherent cal careous perforate Itetk-ularian. 10. CalcarinaSpengleri, Gmel. ; x 10. Tertiary, oicily. Shell dissected so as to show the spiral arrangement of the chambers, and the copious secondary shell substance, a-, a 3, a 4 , chambers of three successive coils in section, showing the thin primary wall (finely tubulate) of each ; b, b, b, b, perforate surfaces of the primary wall of four tiers of chambers, from which the secondary shell substance has been cleared away ; c , c , secondary or intermediate shell substance in section, showing coarse canals ; d, section of secondary shell substance at right angles to c ; c, tubercles of secondary shell substance on the surface ; f,J, club-like processes of secondary shell substance. OitDKii 10. NUMMULIXIDKA, Brady. Characters. Test calcareous and finely tubulated ; typically free, many-chambered, and symmetrically spiral. The higher modifications all possess a supplemental skeleton, and canal system of greater or less complexity. Fain. 1. FUSULININA. Shell bilaterally symmetrical ; chambers extending from pole to pole; each convolution completely enclosing the previous whorls. Shell-wall finely tubulated. Septa single or rarely double ; no true interseptal canals. Aperture a single elongated slit, or a row of small rounded pores, at the inner edge of the final segment. Genera. Fusulina, Fischer; Schwagerina, Mb llcr. Fam. 2. POLYSTOMELLINA. Shell bilaterally symmetrical, nauti- loid. Lower forms without supplemental skeleton or interseptal canals ; higher types with canals opening at regular intervals along the external septal depressions. Genera. Nonionina,, D Orb. ; Folystomdla, Lamarck. Fam. 3. NVMMULITIXA. Shell lenticular or complanate ; lower forms with thickened and finely tubulated shell-wall, but no inter mediate skeleton ; higher forms with interseptal skeleton and com plex canal system. Genera. Archseodiscus, Brady ; Amphistegina, D Orb. ; Opcr- culina, D Orb. ; JIdcrostcgina, D Orb. ; Xummulites, Lamarck ; Assilina, D Orb. Fam. 4. CYCLOCLYPEINA. Shell complanate, with thickened centre, or lenticular ; consisting of a disk of chambers arranged in concentric annuli, with more or less lateral thickening of lami nated shell substance, or acervuline layers of chamberlets. Septa double and furnished with a system of interseptal canals. Genera. Cijdoclij^teus, Carpenter; Orlitoides, D Orb. Fam. 5. EOZOONINA. Test forming irregular, adherent, acervu line masses. Genus. Eozoon Dawson. Further remarks on the Reticularia. The name Thalamophora, pointing to the peculiar tendency which the larger members of the group have to form chamber after chamber and so to build up a complex shell, has been proposed by Hcrtwig (56) and adopted by many writers. The old name Foraminifera (which did not refer to the fine perforations of the Perforata but to the large pscudo- podial aperture leading from chamber to chamber) has also been extended by some so as to include the simpler Gromia-like forms. On the whole Carpenter s term Reticularia (62) seems most suitable for the group, since they all present the character indicated. It has been objected that the Radiolaria are also reticular in their pscudopodia, but if we except the pelagic forms of Reticularia (Globigerina, Orbulina, &c. ), we find that the Radiolaria arc really distinguishable by their stiffer, straighter, radiating pseudopodia. No doubt the Labyrinthulid Chlamydomyxa and the plasmodia of some Mycetozoa are as reticular in their pseudopodia as the Reticularia, but they possess other distinctive features which serve, at any rate in an artificial system, to separate them. The protoplasm of the majority of the Reticularia is unknown, or only very superficially observed ; hence we have made a point of introducing among our figures as ninny as possible which show this essential part of the organism. It is only recently (1876) that nuclei have been detected in the calcareous-shelled members of the group, and they have only been seen in a few cases. The protoplasm of the larger shell-making forms is known to be often strongly coloured, opaque, and creamy, but its minute struc ture remains for future investigation. Referring the reader to the figures and their explanation, we would draw especial attention to the structure of the protoplasmic body of Hastigerina (one of the Globigerinidea) as detected by the &quot;Challenger&quot; naturalists. It will be seen from Fig. XII. 5 that the protoplasm extends as a rela tively enormous &quot;bubbly &quot;mass around the shell which is sunk within it ; from the surface of this &quot; bubbly &quot; (vacuolated or alveol- ated) mass the pseudopodia radiate. The reader is requested to compare this with Fig. XIII., repre senting the &quot;bubbly &quot; protoplasmic body of Thalassicolla. It then becomes obvious that the perforated central capsule CK of the latter holds the same relation to the mass of the protoplasm as does the central perforated shell of Globigerina (Hastigerina). The extreme vacuolation of the protoplasm in both cases (the vacuoles being