58 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



podia. Food is taken into the body at any point, there 

 being no mouth. 



A Foraminifer differs from an amoeba in having an 

 apparently simpler body, the protoplasm being without 

 layers or cavity ; its pseudopodia are long and threadlike, 

 and may unite where they touch each other. It has the 

 property of secreting an envelope, usually of carbonate 

 of lime. The shell thus formed is sometimes of extraor- 

 dinary complexity and singular beauty. In addition to 

 the terminal aperture, it is generally perforated by 



a 



FIG. 2. Rhizopods : a, shell of a monothalamous, or single-chambered, Foraminifer 

 (Lagena. striata) ; b, shell of a polythalamous, or many-chambered, Foraminifer 

 {Polystomella. crispa), with pseudopodia extended ; c, shell of a Radiolarian, one 

 of the Polycystines (Podocyrtzs schomburgkii). 



innumerable minute orifices (foramina) through which 

 the animal protrudes its myriad of glairy, threadlike 

 arms. The majority are compound, resembling cham- 

 bered cells, formed by a process of budding, the new 

 cells being added so as to make a straight series, a 

 spiral, or a flat coil. As a rule, the many-chambered 

 species have calcareous, perforated shells ; and the one- 

 chambered have an imperforated membranous, porce- 

 laneous, or arenaceous envelope. The former are marine. 

 There are few parts of the ocean where these micro- 

 scopic shells do not occur, and in astounding numbers. 



