6o 



PROTOZOA. 



dinium has been thus detected in the Cretaceous formation. 

 With this doubtful exception, however, no Infusorian animal- 

 cule has ever been detected in the fossil state, though the class 

 has doubtless existed from the most remote antiquity. There 

 remain, then, only the three Rhizopodous orders of the Fora- 

 minifera, Radiolaria, and Spongida, all of which secrete hard 

 structures, and all of which are more or less extensively repre- 

 sented as fossils, so that they demand our attention separately 

 and in detail. 



I. FORAMINIFERA. 



The Foraminifera may be denned as Rhizopoda in which the 

 body is protected by a shell or " test" which is usually composed 

 of carbonate of lime, but which may consist of particles of sand 

 cemented together by some animal cement, or may be simply horny 

 (chitinous). The animal may be simple, or may repeat itself inde- 

 finitely by budding, and the body-substance gives out long and 

 thread-like processes (pseudopodia), which interlace with one an- 

 other to form a network, and often coalesce at their bases to form a 

 continuous layer of sarcode outside the shell. The pseudopodia 

 reach the exterior either by perforations in the walls of the shell, or 

 simply by the mouth of the latter (fig. 6, c b\ 



Fig. 6. Morphology of Foraminifera. a Lagena vulgaris, a monothalamous Fora- 

 minifer ; b Miliola (after Schultze), showing the pseudopodia protruded from the oral 

 aperture of the shell ; c Discorbina (after Schultze), showing the nautiloid shell with 

 the foramina in the shell-wall giving exit to pseudopodia ; d Section of Nodosaria 

 (after Carpenter) ; e Nodosaria hispida ; f Globigerina biilloides. 



