CHAPTER VI 

 OTHER PROTOZOA 



i. CLASSIFICATION OF THE PROTOZOA 



" A PROTOZOON is a primitive animal organism usually con- 

 sisting of a single cell, whose protoplasm becomes distributed 

 among many free living cells. These reproduce their kind by 

 division, by budding or by spore formation, the race thus formed 

 passing through different form changes and the protoplasm 

 through various stages of vitality collectively known as the life 

 cycle " (78, p. 17). 



Protozoons may be separated into groups according to the 

 presence or absence of locomotor organs and the character of 

 these when present. Four divisions are usually recognized : 

 (i) Rhizopoda with pseudopodia, (2) Mastigophora with flagella, 

 (3) Infusoria with cilia, and (4) Sporozoa, which are parasitic in 

 cells and without motile organs. 



The size of Protozoa ranges within wide limits. Some are 

 very large, for example, a parasite, Porospora gigantea, which 

 lives in the alimentary canal of the lobster, reaches two thirds of 

 an inch in length; some are just at the limit of vision with the 

 most powerful microscopes, whereas others, like the yellow fever 

 parasite, doubtless exist, though they have never been seen. 

 Individuals belonging to one species vary in size according to 

 their food conditions and age. The variations in structure and 

 life histories of the Protozoa are so numerous as to preclude de- 

 scription in a book of this character. We shall therefore give an 

 abbreviated classification of the phylum and consider typical 

 examples under each class. 



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