CLASSIFICATION- OF THE PROTOZOA. 



48? 



are wholly made up of their remains. The vast chalk 

 beds of Europe and of other countries are almost wholly 



FIG. 735. 



Microscopic Protozoa in Chalk. 



composed of the skeletons of microscopic protozoans 

 mainly Rhizopods. And, according to the estimate of 

 Ehrenberg, the great Prussian microscopist, there are 

 1,000,000 of these organisms in a cubic inch of chalk! 



The Protozoa have been extensively studied and vari- 

 ously classified. Until comparatively recent times they 

 were usually regarded as forming three great groups- 

 Infusoria, Tihizopoda, and Spongida ; but naturalists 

 now recognize six or more great divisions. 



I. SPONGIDA OR PORIFERA : as the Marine and the Fresh-water 



Sponges. 



II. INFUSORIA or Ciliatn, ; as VortirMn, Stentor, Pammecimn, etc. 



III. FLAGELLATA (including Noctilucae?) ; as the Monads. 



