66 MANUAL OF ZOOLOGY. 



blunt and lobose character of the pseudopodia in the Arcellina 

 would, however, appear to be a more important character than 

 the possession of a test, and would assign to these forms a 

 position close to Amoeba. 



CHAPTER III. 

 FORAMINIFERA. 



ORDER III. FORAMINIFERA. The Foraminifera may be de- 

 fined as Rhizopoda in which the body is protected by a shell or 

 " test" composed of carbonate of hme, or of sand-grains cemented 

 together, or, rarely, of chitine ; there is no distinct separation of the 

 sarcode of the body into ectosarc and endosarc, and a nucleus and 

 contractile vesicle are present in at any rate some cases. The 

 pseudopodia are long and filamentous, and interlace with one an- 

 other to form a network. 



The Foraminifera are specially characterised by the posses- 

 sion of a "test" or external shell, which is usually composed 

 of carbonate of lime, but is often composed of grains of sand 

 or other adventitious solid particles cemented together by 

 animal matter, or which, as in Gromia, may be simply chitin- 

 ous. The test may be composed of an aggregation of cham- 

 bers or "loculi" (fig. n, c), or of a single chamber only, and its 

 walls are usually pierced by numerous pores or " foramina" 

 through which the pseudopodia are protruded ; the place of 

 these being in other forms supplied by the large size of the 

 terminal, or "oral" aperture of the shell (fig. 10, b), the walls 

 themselves being imperforate. The presence or absenceof 

 foramina in the shell-walls is believed to constitute a genuine 

 structural distinction, and the Foraminifera may be thereby 

 divided into two great groups (Perforata and Imperforata). 



As regards the soft parts of the Foraminifera, the body is 

 composed of extensile and contractile sarcode usually red- 

 dish or yellowish in colour which not only fills the interior of 

 the shell, but generally invests its outer surface also with a thin 

 film, from which the pseudopodia are emitted (fig. 10, b). The 

 test, therefore, in this case, is not a true cuticular secretion, 

 like that of the Mollusca, but it is truly immersed within the 

 sarcode of the body. The sarcode is not differentiated into a 

 distinct ectosarc and endosarc, and until recently was believed 

 to be devoid of a nucleus and contractile vesicle, and, indeed, 



