ECONOMIC ZOOLOGY 



CHAPTER I 

 PROTOZOA 



The phylum Protozoa includes a large number of small animals; 

 they are mostly of microscopic size, though some of them are easily 

 seen with the naked eye. They all consist of but a single cell, which 

 is sometimes quite complex. 



The phylum is usually divided into four classes according to the 

 presence or absence of organs of locomotion and the character of these 

 organs, if present. These classes are as follows: 



I. Rhizopoda, with pseudopodia, Fig. i. II. Mastigophora, with 

 flagella, Fig. 2. III. Sporozoa, non-motile, in adult condition at 



PIG. i. Ameba. cv, contractile vacuole; ec, ectosarc; en, endosarc; fv, food 

 vacuole; n, nucleus; p, pseudopodia. Highly magnified. 



least, Fig. 4. IV. Infusoria, with cilia. Of these classes the first 

 three are of economic importance and will be discussed in turn, the 

 Infusoria are of little importance, though some of them may be con- 

 cerned in certain intestinal diseases. 



Rhizopoda. Without further classification several representatives 

 of^this class will now be discussed. 



Ameba, Fig. i . There are two (possibly more) species of this familiar 

 genus that are found in the human intestine, Ameba or Entameba coli 



