Protozoa. 2 1 



As the protoplasm includes its food in the manner 

 described, foreign particles and fine granules become 

 enclosed in it derived from the undigested parts of the 

 food. Sometimes drops of water or of thin fluid may 

 be seen in the protoplasm like little bubbles ; these 

 are called vacuoles (fig. 14), and they with the gran- 

 ules circulate actively in the body mass ; obscure con- 

 densed points or nuclei also exist, and the name of 

 the class is derived from the root-like spreading of the 

 pseudopodia. 



Mode of Growth of Rhizopoda. Those Rhizo- 

 pods that separate lime from the sea-water to form 

 shells, begin the process while they are young single 

 masses, and they increase by budding, each bud 

 forming on the newest FIG. 9. 



end of the last bud ; 

 consequently the 

 perfect animal con- 

 sists of a rod-like or 

 spiral set of chambers, 

 each chamber being a 

 new, undetached bud. 



Two forms of Protozoa. Protamceba pri- 

 DUOS DeCOme mltiva, the simplest living animal ; Mago- 



, sphtera planula, a compound form. 



quite separate and 

 grow into new individuals. In a few cases each 

 bud becomes detached, so that the animals always 

 remain of one chamber. 



Shell-forming Rhizopods are occasionally aggre- 

 gated in great masses and sometimes at great depths in 

 the ocean. Such seems to have been their habit in 

 past times, and many of the chalky limestones consist 

 of the accumulated shells of Foramimfera. 



