P E T O Z A. 



CHAPTER I. 



PROTOZOA. 

 1, General characters. — 2. Classification. 



I. Cresieral eliaraeters. — The sub-kingdom 

 Protozoa includes a number of animal beincfs of 

 simple organisation, many of which have, until 

 recently, been associated with the lower members 

 of the vegetable kingdom. Hence no good ge- 

 neral definition can be given of this sub-kingdom, 

 the several forms which it includes being distin- 

 guished from those which are placed in the four 

 remaining zoological departments by chiefly nega 

 tive characters. In none ot the Protozoa do we 

 find a nervous system or organs of sense, and, 

 in many of- these animals, the existence of a 

 distinct alimentary apparatus has yet to be ascer- 

 tained. 



In the substance of the bodies of most Protozoa 

 a minute solid particle known as the ' nucleus ' is 

 found to occur ; and, in addition to this, the pre- 

 sence of certain clear spaces termed 'contractile 

 vesicles ' may, in some species, be traced, 



B 



