24 MANUAL OF ZOOLOGY SECT. 



ing protoplasm, and sometimes produced into a number of 

 relatively large spines. 



Though the great majority of Foraminifera have dense 

 shells composed of carbonate of lime, there are many in 

 which the shell resembles that of Difflugia in being com- 

 posed of foreign particles, such as sand-grains, cemented 

 together ; these are termed the arenaceous Foraminifera ; 

 some of these have one large opening, some a number of 

 pores. In certain fresh-water forms, such as Gromia, the 

 shell is chitinoid. In Gromia (Fig. 4, /) the chitinoid shell 

 has a wide mouth through which the protoplasm protrudes 

 to form a layer enclosing the shell and giving off the 

 pseudopodia. 



Little is known of the reproduction of the Foraminifera. 

 But in some a remarkable mode of reproduction has been 

 observed. The protoplasm in the interior of the shell divides 

 up into a number of particles. Each of the bodies thus 

 formed possesses, instead of pseudopodia, a single delicate 

 whip-like appendage — the flagellum — which lashes to and 

 fro and propels the embryo Foraminifer through the water. 

 Such a flagellum-bearing embryo is termed a flagellula. 



All the Foraminifera, with the exception of Gromia and 

 one or two allied forms, are marine, and the greater number 

 are pelagic — i.e., live in the surface waters of the open sea — 

 though they occur also inshore, and at almost all depths. 

 The pelagic Foraminifera are most abundant in warm lati- 

 tudes, where they occur in enormous numbers. The ocean 

 floor at depths of five hundred to twenty-eight hundred 

 fathoms is covered in many places with a mud-like deposit 

 which effervesces and dissolves when acid is added, and 

 which, when examined under the microscope, is found to 

 consist mainly of the shells of Foraminifera, which must 

 have fallen down from above on the death of the animals. 



