18 PROTOZOA RHIZOPODA CLASS i 



Order 1. FORAMINIFERA. d'Orbigny. 1 

 (Polythalainia, Breyn ; Thalamophora, Hertwig.) 



Rhizopoda with slender, thread-like, or band-like, frequently anastomosing pscm/n- 

 podia, and usually with a calcareous, more rarely with an arenaceous or chitinous test. 



The scarcely differentiated, richly granulated sarcode body of the 

 Foraminifera usually contains a contractile vacuole, and is enclosed by a shell 

 or test which is almost invariably calcareous in composition, although in some 

 cases it may be of a silicious or even chitinous nature, and which, as a rule, is 

 divided into chambers by interior partitions or septa. The sarcode com- 

 municates with the exterior either by means of a single large aperture (oral 

 or general aperture) situated at one extremity of the test, or by means of 

 innumerable fine pores (foramina) which perforate the shell. Through these 

 openings the sarcode emits usually long, filiform, net -like anastomosing 

 pseudopodia, in which often active granular currents are discernible. 



Only a few forms secreting chitinous tests (Gromia) are fresh- water inhabit- 

 ants ; the rest are marine in habit. Foraminifera are usually so small in size 

 that, although perceptible to the naked eye, they can barely be discriminated 

 as separate individuals. Certain exceptionally large forms (Nummulites) attain 

 a diameter of four or five centimetres. 



intermingled with decomposed organic matter. In deep-sea ooze, which consists chiefly of lime 

 carbonate, as well as in Bathybius, great quantities of minute calcareous bodies of various shapes 

 are found, such as also occur as an essential constituent of chalk, marls, and most marine lime- 

 stones belonging to older geological periods (cf. C. W. Giimbel, Neues Jahrbuch fiir Mineralogie, 



1870, p. 753). Ehrenberg 

 termed these bodies morpho- 



>j^ ^ju ^ lites, and regarded them as 



K/J PfiMiM$\ \ inorganic in nature. Huxley 



(Journal Microscop. Science, 



fcfclBl UN i *JS 1868, VIII. No. 6) and Haeckel 



(Jenaische Zeitschrift, 1870, 

 V. 3, p. 18) regarded them at 

 first { 



FIG. 1, c.Coccoliths (Discoliths) from the Adriatic Sea ; upper side and (Fig. 1). The simple, disk- 

 in profile (after O. Schmidt). like varieties, convex on the 



FIG. 2. Coccospheres from the Atlantic Ocean (after Haeckel). iinnpr sulp iurl rnnpavp nn tin- 



FIG. 3.-Rhabdoliths from the Adriatic Sea (after O. Schmidt). All " 



figures magnified 700 diameters. low er, were termed discoliths 



(Fig. 1, a, b) ; while those com- 

 posed of two closely applied disks of different sizes, resembling cuft'-buttons in profile, were referred 

 to as cyatlwliths (Fig. 1, c). Coccoliths are only visible under powers of 800 1000 diameters, and 

 exhibit, as a rule, a number of zones differing in their refractive indices, which are disposed about a 

 single, double, or star-shaped central granule. Frequently large numbers of coccoliths become 

 aggregated together in the form of freely suspended spherules or coccospheres (Fig. 2). Besides 

 coccoliths, other minute, rod-shaped, calcareous bodies are sometimes met with, which are charac- 

 terised by a discoidal or cruciform enlargement at one end. These are called rlitdxInUtli* (Fig. 3), 

 and their nodular aggregations rhabdospheres. Wyville Thomson, Carter, and Murray would 

 identify coccospheres as unicellular algae, or as sporangia of algae, while Haeckel creates for them 

 a special group, " Calcocytae," and assigns them provisionally to the Protophytes. According 

 to Harting, however, the action of ammonia generated by the decomposition of albuminous matter 

 held in solution in lime sulphate or lime chloride, causes the separation out of minute calcareous 

 disks which bear a striking resemblance to coccoliths. Hence it would appear that the formation 

 of excessively fine divided particles of lime in the sea should take place wherever there are decom- 

 posing albuminous, or nitrogenous substances present, and the calcium sulphate held in solution in 

 the water becomes precipitated as calcium carbonate. 



1 Literature : 

 d'Orbigny, Atcide, Foramiuiferes fossiles du Bassiu tertiaire de Vienne, 1846. 



