1 
Division V. PROTOZOA. 
This last Division of the Animal Kingdom includes a number of creatures of a very low type 
of organization, whicli 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. 
Tt is in vain to seek in these creatures for any internal organs. Nearly all live in water ; a 
few only 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 Rkizopoda. 
* "All the forms represented in the engraving are found in nature; most of them are common in the water of the 
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 Inf usoria, which 
we are about to notice, but species of Botifera and RMzopoda abound in common water. 
