,,KI,KK i FOBAMINIPEBA 1!) 



The test may be either unilocular, enclosing a single cavity (Monothalamia), 

 or it may be divided by septa into a greater or lesser number of chambers 

 (Poli/thalamia). Multilocular tests all grow from a single primordial chamber, 

 which is either spheroidal or elliptical in contour, and augment rapidly by 

 means of the successive apposition of new chambers, each a little larger than 

 the first, and each being applied in turn against the general pseudopodial 

 aperture of the preceding. All the chambers communicate with each other by 

 means of pores through which the sarcode is protruded. According as the 

 chambers are applied against one another in a linear series (Stichostega), in a 

 spiral (Helicostega), in concentric rings (Cyclostega), in double or triple alterna- 

 tions of either straight (Enallostega) or spiral rows (Entomostega), or envelop 

 one another in irregular coils disposed in from two to five different planes 

 (Aguthistega), a great variety of forms may be produced. These differences 

 in external form, together with peculiarities in the mode of growth, were 

 employed by Alcide d'Orbigny as a basis for the first detailed system of 

 classification of the Foraminifera that has been devised. For specific diag- 

 noses, the relative size and shape of the shell, and varieties of ornamentation, 

 such as bands, lips, protuberances, points, spines, and the like, are of greatest 

 significance. 



In certain Foraminifera which secrete calcareous shells (Nummulinidae, 

 Miliolidae, Lagenidae, Orbulina) a peculiar dimorphism has been observed, in that 

 while some individuals have an extremely 

 large primordial chamber (megasphere), 

 others, although differing in nowise in 

 external form and ornamentation, are 

 characterised by an extremely minute 

 1 n-imordiat chamber (microsphere, Fig. 4). 

 Those individuals which possess mega- 

 spheres are almost invariably much 



inferior in size to those having micro- Fia 4 . 



spheres. De la Harpe refers this pheno- woeuMna /;//j/i, schiumb. Recent ; Bay of 

 menon to sexual differences; Munier- 

 Chalmas and Schlumberger claim, on 

 the other hand, that during the growth of those forms characterised by 

 microspheres, the megaspheres, which are in all cases originally present, 

 become absorbed and are replaced by an increased number of smaller 

 chambers. Van den Broeck argues against these hypotheses, and attempts 

 - to explain dimorphism as the result of different modes of reproduction (fission 

 and budding). 



The finer structure of the shell or test, which has been thoroughly 

 investigated by Carpenter and Williamson, is of great importance in the 

 classification of the Foraminifera. 



Chitinow tests are as a rule single -chambered (monothalamous), imper- 

 forate, and are provided with a single large-sized oral aperture. Silicious 



I'.ln-.-tiberg, C. Gf., Mikrogeologie, 1854, and Abhandlungeu der Berliner Akademie, 1839. 



X-lni/tze, Max, Ueber den Organismus der Polythalamien, Leipzic, 1854. 



Carpenter, W. B., Introduction to the Study of the Foraminifera, Ray Society, 1862. 



Reuss, E. A., Numerous Reports in Sitzuugsberichte der Wiener Akademie, from 1860 onwards. 



,NV// t'-ni/,',; (',>,i rtid, Saggio di una Classificazione dei Foraminiferi, Bollet. Comitato Geol., 1876. 



Jinx///, II'. /;., Monograph of Carboniferous and Permian Foraminil'era, Palaeontograph. Soc., 1876. 



Brady, Jr. B., Report on the Foraminifera, Scientific Results Challenger Exped., Zoology, XL, 1884. 



