DIVISION V. PliOTOZOA. 



645 





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CONTENTS OP A D!:or CF WATl.K, /.S SELX TY THE JIICROSCOPE.* 



Division V. PROTOZOA. 



This last Division of the Animal Kingdom includes a number of creatures of a very low type 

 of organization, which appear almost to occupy a sort of neutral ground between animals and 

 vegetables. Their bodies consist either of a simple elementary cell, with its contents, or of an 

 aggregation of several of these cells ; each, however, still appearing to retain its independent 

 existence. They are generally of very minute size, and only to be observed with the microscope. 

 It is in vain to seek in these creatures for any internal organs. Nearly all live in water; a 

 few oidy inhabit the intestines of other animals. They generally present the appearance of a 

 transparent gelatinous cell, the substance of which they are composed being called sarcode. 

 Some of them are propagated by a division of the substance of which their bodies are formed ; 

 others by a kind of gemmation, and others in still different ways. They all live by imbibing 

 fluids through their outer surface, or by the amalgamation of solid substances with the gelati- 

 nous mass of which they consist. 



Referring the reader to our brief description of the physiology of the Protozoa, Vol. I., p. 17, 

 and to our classification, p. 30, we proceed to notice them under the three classes of Infusoria., 

 Porifera., and Rhizojwda. 



* "All the forms represented in the engravino; are found in nature; most of them are common in the water of (he 

 Thames, at London, and many of them in our Croton water. They are generally very active, some of them shooting 

 about like arrows, and others writhing, tossing, and tumbling like harlequins. Many of these creatures bear the 

 most hideous forms, and others possess the fiercest and most predaceous appetites. Nevertheless, we swallow thou- 

 sands of them daily, not with impunity merely, but with the highest relish. Not only species of the Infusoria, which 

 we are about to notice, but species oi Botlfera and Bhizopoda abound in common water. 



