CHAPTEK I 

 PHYLUM I. : THE PROTOZOA 



THE Protozoa are the simplest animal forms known ; in them 

 the whole living body consists of a single speck of the jelly- 

 like living substance, Protoplasm, the body being so minute 

 as to be in nearly all cases invisible to the naked eye. 

 Because of their simple delicate structure, and their lack of 

 special organs for carrying on the different vital functions of 

 the body, these Protozoan organisms are able to exist only 

 under special limited conditions, and are nearly all to be 

 found living in water, fresh or salt, though some are parasitic 

 in the tissues of other animals. 



In this group are included all the naked unicellular forms 

 such as the fresh- water Amoeba and Yorticella, and also those 

 marine forms such as Globigerina, which secrete round their 

 bodies calcareous shells. 



Type : The Amoeba, or Proteus Animalcule. 



This simplest of animals is unfortunately so small, that a 

 microscope is necessary for its examination. However, an 

 understanding of certain points in its structure, and of its 

 vital processes, is so helpful as a basis for the study of more 

 complex forms, that it is well, if possible, to acquire some 

 practical knowledge of it, when commencing the study of 

 different types of animal life. 



Amoebae are to be found very abundantly in the mud at 

 the bottom of most ponds, but as each individual is only about 

 T ^th of an inch in diameter, a microscope with a high mag- 

 nifying power is needed to render its structure visible. 



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