884 THE ANIMAL KINGDOM. 



Yellow cells, Brandt, op. cit. supra, pp. 65-71 ; Id. Mitth. Zool. Stat. Naples, 

 iv. 1883, p. 220, p. 235 ; Geddes, Nature, xxv. 1881-2, p. 303. 



Distribution and Fossil forms, Haeckel, Challenger Reports cited supra, pp. 

 cxlvi-clxxv. with lit. quoted. 



CLASS FORAMINIFERA. 



(Reticularia ; Thalamophora^) 



Rhizopod Protozoa with long branching and anastomosing pseudopodia 

 which show well-marked granule -sir earns. The protoplasm is of a Uniform 

 character throughout the body ; the nucleus single ; contractile and non- 

 contractile vacuoles are very rare. A test or shell is invariably present either 

 chitinoid, calcareous or adventitious ; it presents many varieties of shape and 

 structure. Reproduction is typically effected by the multiplication of the 

 nucleus, the separation of a portion of protoplasm round each nucleus so 

 formed, and its inclosure by a test. Chiefly marine ; a few freshwater. 



The test is the most prominent feature of the Foraminifera. It is 

 chitinoid in the Gromidae ; very delicate in Lieberkiihnia, stouter but 

 flexible in Gromia itself, resistent in Microgromia, and in Diaphoropodon 

 incrusted with diatom shells, &c. It is hyaline or somewhat yellow ; 

 ovate with a single terminal aperture, except in Shepheardella, where it 

 is a tube with an aperture at both ends. There is reason to suppose that 

 it is porous in Diaphoropodon *. 



A calcareous test is characteristic of the Miliolidae, Textularidae, 

 Cheilostomellidae, Lagenidae, Globigerinidae, Rotalidae and Nummulinidae. 

 In the Miliolidae its substance is compact in texture, homogeneous with 

 a polished white or ' porcellanous ' appearance by reflected light, in thin 

 shells, or in thin sections viewed by transmitted light, amber-coloured. 

 Young specimens are opalescent and diaphanous. In the other families 

 above-named the substance of the test is traversed by fine vertical pores, 

 varying in diameter and sometimes of two different sizes in the same 

 test, e. g. in Orbulina and some other Globigerinidae, often laminated and 

 in thin tests or sections transparent or hyaline. When the test is thin, 

 and its pores relatively far apart and wide, it has a vitreous aspect ; when 

 thick, the pores fine and close set, it is milky and semiopaque. Some 

 are perfectly opaque like Calcarina, and this is always the case if they are 

 dead and have been lying long in sea-water. Owing to the absence of 

 pores the Miliolid test is often termed * imperforate,' that of the other 



1 The test of Microgromia withstands the action of concentrated acids and alkalies ; it is perhaps 

 silicified. The short hyaline simple processes fringing the body of Diaphoropodon appear to be 

 pseudopodial (Archer, Q. J. M. ix p. 396). 



