34 INVERTEBRATE ANIMALS. 



mated spider's web." Lastly, the microscope reveals in the 

 pseudopodia a very curious circulation of minute solid parti- 

 cles or granules, which travel in all directions through the 

 pseudopodial net-work. Internally, the sarcode-body of the 

 Foraminifera exhibits absolutely no structures or definite or- 

 gans of any kind. Even the nucleus and contractile vesicle 

 which occur in the Amoeba are here absent, and the only traces 

 of structure are to be found in the existence of scattered gran- 

 ules. 



Simple as is the sarcode-body of the Foraminifera, it has 

 in all cases the power of secreting a skeleton or shell, which 

 is technically called the "test" (Lat. testa, a shell). The 

 shell is usually " calcareous " that is to say, composed of car- 

 bonate of lime ; but it is sometimes " arenaceous," or com- 

 posed of particles of sand united together firmly by an un- 

 known animal cement. In either case, the shell may exhibit 

 one or other of two very distinct types of structure. In the 

 one type (as in Miliola, Fig. 4, b), the shell- walls are not per- 



FIG- 4. Morphology of Foraminifera. a Lagena vulgaris, a monothalamous Foraminifcr ; 

 b Miliola (after Schultze), showing the pseudopodia protruded from the oral aperture of 

 the shell ; c DiscorMna (after Schultze), showing the nautiloid shell with foramina in 

 the shell- walls, giving exit to pseudopodia ; d Section of Nodosaria (after Carpenter) ; 

 e Nodosaria hispida ; f Globige/rina bulloides, 



forated with holes, and the pseudopodia are therefore all 

 emitted from the mouth of the shell. In the other type (as in 



