534 



CONCLUDING REMARKS. 



during all the ages since its first appearance upon the 

 earth. When we consider the classes, the orders, the 

 families, the genera, the vast number of living and per- 

 haps the much greater number of extinct species, and 

 then consider that each species is represented in many 

 cases by millions of individuals, and that probably no two 



by some eminent naturalists to constitute a fifth branch of the Animal 

 Kingdom, called PROTOZOA. These organisms are almost wholly aquatic, 

 and, excepting the Sponges, are mainly exceedingly minute. The Protozoa 



Fig. 534- 



Podocyrtis Schomburgkii. 



Fig. 535- 



ig. 53*- 



Amoeba radiosa. 



Polystomella crispa. 



Fig. 538. 



Nummulites lenticnlaris 

 Section. 



Fig- 539- 



Sponge, in action. Sponge 



include three groups, which have been much divided and subdivided by 

 authors : Infusoria, of which Vorticella, Fig. 529, is a prominent exam- 

 ple ; Rhizopoda, including Foraminifera, Figs. 535-537; and Spongidse, 

 or Sponges, well known to all, Figs. 538, 539. 



