250 PROTOZOANS. 



prized, have all come from the skeletons of these little 

 flower-like animals of the sea. Their skeletons have 

 furnished even the blocks of marble ■which the sculp- 

 tor chisels, and are thus inseparably linked with the 

 highest department of culture and of art in which the 

 mind and hand of man can engage. 



PROTOZOANS. 



There is a vast mimber of beings which are so 

 simple in their structure that naturalists are in doubt, 

 in many cases, whether to call them Plants or Ani- 

 mals. These are now called Protozoans, a word which 

 means first or simplest animals. A few of the forms 

 are shown in Figures 510-520, — all much enlarged, 

 except Figures 518, 519, 520. In most cases they 

 have neither mouth nor stomach, and, excepting the 

 Sponges and some others, are exceedingly minute and 

 mostly microscopic. They are doubtless more numerous 

 than all the other animals of the globe, for they live 

 in immense numbers in every ditch and pool, every 

 stream, pond, and lake, and in almost every part of the 

 sea. There is scarcely a drop of water that is not in- 

 habited by some of them. They were also exceed- 

 ingly abundant in the past ages of the world ; for their 

 skeletons, or hard parts, fill the rocks in many places, 

 and rocky strata hundreds of feet in thickness are 

 wholly made up of their remains. 



One group of the Protozoans is called Infusoria, 

 from having first been found in vegetable infusions, 

 that is, in liquids in which plants have been immersed ; 

 of these, Vorticella, Figure 510, is a well-known kind. 



There is another group called Rhizopods — a word 



