 | |
| Fig. 19.—Arenaceous Foraminifera. | |
a, Exterior of Saccammina. b, The same laid open. c, Portion of test more highly magnified. d, Pilulina. | e, Portion of test more highly magnified. f, Nautiloid Lituola, exterior. g, Chambered interior. h, Portion of labyrinthic chamber wall, showing component sand-grains. |
| Fig. 20.—Section of Fusulina Limestone. |
| Fig. 21.—Microscopic Organisms in Chalk from Gravesend. a, b, c, d, Textularia globulosa; e, e, e, e, Rotalia aspera; f, Textularia aculeata; g, Planularia hexas; h, Navicula. |
The pelagic floating genera are also specially modified. Their shell is either thin or extended many times by long slender tapering spines, and the protoplasm outside has the same character as that of the Radiolaria (q.v.), being differentiated into jelly containing enormous vacuoles and traversed by reticulate strands of granular protoplasm. These coalesce into a peripheral zone from which protrude the pseudopods, here rather radiate than reticulate. Most genera and most species are cosmopolitan; but local differences are often marked. Foraminifera abound in the shore sands and the crevices of coral reefs. The membranous shelled forms decay without leaving traces. The sandy or calcareous shells of dead Foraminifera constitute a large proportion of littoral sand, both below and above tide marks; and, as shown in the boring on Funafuti, enter largely into the constituents of coral rock. They may accumulate in the mud of the bottom to constitute Foraminiferal ooze. The source of these shells in the latter case is double: (1) shells of bottom-dwellers accumulate on the spot; (2) shells of dead plankton forms sink down in a continuous shower, to form a layer at the bottom of the ocean, during which process the spines are dissolved by the sea-water. Thus is formed an ooze known as “Globigerina-ooze,” being formed largely of that genus and its ally Hastigerina; below 3000 fathoms even the tests themselves are dissolved. Casts of their bodies in glauconite (a green ferrous silicate, whose composition has not yet been accurately determined) are, however, frequently left. Glauconitic casts of perforate shells, notably Globigerina, have been found in Lower Cambrian (e.g. Hollybush Sandstone), and the shells themselves in Siberian limestones of that age. It is only when we pass into the Silurian Wenlock limestone that sandy shells make their appearance. Above this horizon Foraminifera are more abundant as constituents, partial or principal of calcareous rocks, the genus Endothyra being indeed almost confined to Carboniferous beds. The genus Fusulina (fig. 20) and Saccammina (fig. 19) give their names (from their respective abundance) to two limestones of the Carboniferous series. Porcellanous shells become abundant only from the Lias upwards. The glauconitic grains of the Greensand formations are chiefly foraminiferal casts. Chalk is well known to consist largely of foraminiferal shells, mostly vitreous, like the north Atlantic globigerina ooze. In the Maestricht chalk more littoral conditions prevailed, and we find such large-sized species as Orbitoides (vitreous) and Orbitolites (porcellanous; figs. 5, 6), &c. In the Eocene Tertiaries the Calcaire Grossier of the Paris basin is mainly composed of Miliolid forms. Nummulites occur in English beds and in the Paris basin; but the great beds of these, forming reef-like masses of limestone, occur farther south, extending from the Pyrenees through the southern and eastern Alps to Egypt, Sinai, and on to north India. The peculiar structure occurring in the Lower Laurentian limestone, as well as other limestones of Archean age described as a Nummulitaceous genus, “Eozoon,” by Carpenter and Dawson, and abundantly illustrated in the 9th edition of his encyclopaedia, is now universally regarded as of inorganic origin. “Looking at the almost universal diffusion of existing Foraminifera and the continuous accumulation of their shells over vast areas of the ocean-bottom, they are certainly doing more than any other group of organisms to separate carbonate of lime from its solution in sea-water, so as to restore to the solid crust of the earth what is being continuously withdrawn from it by solution of the calcareous materials of the land above sea-level.” (E.R. Lankester, “Protozoa,” Ency. Brit. 9th ed.)
| Fig. 22.—Imperforata. |
| 1, Spiroloculina planulata, Lamarck, showing five “coils”; porcellanous. 2, Young ditto, with shell dissolved and protoplasm stained so as to show the seven nuclei n. 3, Spirolina (Peneroplis); a sculptured imperfectly coiled shell; porcellanous. 4, Vertebralina, a simple shell consisting of chambers succeeding one another in a straight line; porcellanous. 5, 6, Thurammina papillata, Brady, a sandy form. 5 is broken open so as to show an inner chamber; recent. × 25. 7, Haplophragmium canariensis, a sandy form; recent. 8, Nucleated reproductive bodies (bud-spores) of Haliphysema. 9, Squamulina laevis, M. Schultze; × 40; a simple porcellanous Miliolide. 10, Protoplasmic core removed after treatment with weak chromic acid from the shell of Haliphysema tumanovitzii, Bow. n, Vesicular nuclei, stained with haematoxylin. (After Lankester.) 11, Haliphysema tumanovitzii; × 25 diam.; living specimen, showing the wine-glass-shaped shell built up of sand-grains and sponge-spicules, and the abundant protoplasm p, issuing from the mouth of the shell and spreading partly over its projecting constituents. 12, Shell of Astrorhiza limicola, Sand.; × 3⁄2; showing the branching of the test on some of the rays usually broken away in preserved specimens (original). 13, Section of the shell of Marsipella, showing thick walls built of sand-grains. |
| Fig. 23.—Perforata. |
| 1, Spiral arrangement of simple chambers of a Reticularian shell, as in small Rotalia. 2, Ditto, with double septal walls, and supplemental shell-substance (shaded), as in large Rotalia. 3, Diagram to show the mode in which successively-formed chambers may completely embrace their predecessors, as in Frondicularia. 4, Diagram of a simple straight series of non-embracing chambers, as in Nodosaria. 5, Hastigerina murrayi, Wyv. Thomson, a, Bubbly (vacuolated) protoplasm, enclosing b, the perforated Globigerina-like shell (conf. central capsule of Radiolaria). From the peripheral protoplasm project, not only fine pseudopodia, but hollow spines of calcareous matter, which are set on the shell, and have an axis of active protoplasm. Pelagic; drawn in the living state. 6, Globigerina bulloides, d’Orb., showing the punctiform perforations of the shell and the main aperture. 7, Fragment of the shell of Globigerina, seen from within, and highly magnified, a, Fine perforations in the inner shell substances; b, outer (secondary) shell substance. Two coarser perforations are seen in section, and one lying among the smaller. 8, Orbulina universa, d’Orb. Pelagic example, with adherent radiating calcareous spines (hollow), and internally a small Globigerina shell. It is probably a developmental phase of Globigerina, a, Orbulina shell; b, Globigerina shell. 9, Polytrema miniaceum, Lin.; × 12. Mediterranean. Example of a branched adherent calcareous perforate Recticularian. 10, Calcarina spengleri, Gmel.; × 10. Tertiary, Sicily. Shell dissected so as to show the spiral arrangement of the chambers, and the copious secondary shell substance. a², a³, a4, 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′; e, tubercles of secondary shell substance on the surface; f, f, club-like processes of secondary shell substance. |
Historical.—The Foraminifera were discovered as we have seen by A. d’Orbigny. C.E. Ehrenberg added a large number of species, but it was to F. Dujardin in 1835 that we owe the recognition of their true zoological position and the characters of the living animal. W.B. Carpenter and W.C. Williamson in England contributed largely to the study of the shell, the latter being the first to call attention to its multiform character in the development of a single species, and to utilize the method of thin sections, which has proved so fertile in results. W.K. Parker and H.B. Brady, separately, and in collaboration, described an enormous number of forms in a series of papers, as well as in the monograph by the latter of the Foraminifera of the “Challenger” expedition. Munier-Chalmas and Schlumberger brought out the fact of dimorphism in the group, which was later elucidated and incorporated in the full cytological study of the life-cycle of Foraminifera by J.J. Lister and F. Schaudinn, independently, but with concurrent results.
Literature.—The chief recent books are: F. Chapman, The Foraminifera (1902), and J.J. Lister, “The Foraminifera,” in E.R. Lankester’s Treatise on Zoology (1903), in which full bibliographies will be found. For a final résumé of the long controversy on Eozoon, see George P. Merrill in Report of the U.S. National Museum (1906), p. 635. Other classifications of the Foraminifera will be found by G.H. Theodor Eimer and C. Fickert in Zeitschr. für wissenschaftliche Zoologie, lxv. (1899), p. 599, and L. Rhumbler in Archiv für Protistenkunde, iii. (1903-1904); the account of the reproduction is based on the researches of J.J. Lister, summarized in the above-cited work, and of F. Schaudinn, in Arbeiten des kaiserlichen Gesundheitsamts, xix. (1903). We must also cite W.B. Carpenter, W.K. Parker and T. Rymer Jones, Introduction to the Study of the Foraminifera (Ray Society) (1862); W.B. Carpenter, “Foraminifera,” in Ency. Brit., 9th ed.; W.C. Williamson, On the Recent Foraminifera of Great Britain (Ray Society), (1858); H.B. Brady, “The Foraminifera,” in Challenger Reports, ix. (1884); A. Kemna, in Ann. de la soc. royale zoologique et malacologique de Belgique, xxxvii. (1902), p. 60; xxxix. (1904), p. 7.