PROTOZOA: FORAMINIFERA. 53 



CHAPTER in, 



FORAMINIFERA. 



Order III. Foraminifera. — The Foraminifera may be 

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

 "test" tisually composed of carbonate of lime ; there is no distinct 

 separation of the sarcode of the body into ectosarc and endosarc, 

 and the nucleus and contractile vesicle are both absent. The pseu- 

 dopodia are long and filamentous, and interlace with one another 

 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 soHd particles cemented together by 

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

 ous. (If Lieberkiihnia is to be regarded as a Foraminifer, the 

 possession of a test cannot be looked upon as essential, since 

 this animalcule is naked. The Monera, also, differ from the 

 present group mainly, if not altogether, by their naked and 

 unprotected bodies.) The test is usually composed of an 

 aggregation of chambers or " loculi " (fig. 4, c), and its walls 

 are usually pierced by numerous pores or " foramina " through 

 which the pseudopodia are protruded ; the place of these 

 being in some forms supplied by the large size of the terminal, 

 or " oral," aperture of the shell (fig. 4, b). The presence or 

 absence of 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 Imper- 

 forata). 



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. The test, there- 

 fore, 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 is devoid of a. nucleus and contractile 

 vesicle, and, indeed, of any organs or specialised parts of any 

 kind. From this uniformity in its composition there seems 

 some reason to conclude that the Foraminifera — in spite of the 

 complexity and mathematical regularity of many of their shells 



