THE PROTOZOA. 



135 



shells, in which there are fine holes or foramina 

 traversed by threads of protoplasm. The dead shells 

 of Forarainifera of this type compose the ooze of the 

 Atlantic bed; and the ooze of past geological 

 pfiriods, known to us in the form of chalk, is also 





Fig. 25, -A ^ .^^^mulite : a, exterior ; b, seen in section, 



composed of the same material. The largest of the 

 fossil Forarainifera is called the Nummulite (fig. 25), 

 or money stone, from its round shape. It is found so 

 abundantly in the limestone of the Eocene period, 

 that the limestone has thence received its name, and 



^=^ ^^^ C^CJ O^ff . 



Fig. 27. 



-Fi^. 23.— Magnified spsclmens of ^mosba (small ones): cu, contractile vacuole; 

 n, nndeus ; ps, pseadopodia; /, small organisms taken in as food. Th.e tlu:ee ' 

 smaller specimens are ahovfm. in a more or less retracted state, the two larger 

 ones more fictive. All show an inner granular layer, the 6ndoplasm, and an 

 outer clear layer, the ectoplasm. (The boiindarj line between these appears in , 

 the cut somewhat too distinctly marked.) 



Fig. 27. — Changes of outline presented by a single Amceba : 1 to 16, during a 

 period of four minutes ; 17 to 26, during a furiher period of three minutes. 



is called the Nummulite limestone. The Rhizopoda 

 also include the soft shell-less Amoeba-like forms, of 



