PROTOZOA. 



6 9 



will be well to consider the protozoa as a class and to study the char- 

 racters which all have in common. 



STRUCTURE OF THE PROTOZOA. 



Most protozoa are microscopical; some of them are visible to the 

 naked eye as individuals, or as agglomerated masses of individuals. For 

 example, the Sarcosporidia, which occur in the muscles of mice and other 

 animals, can easily be seen without a microscope, and the huge plasmodial 

 masses of Amoeba, which are sometimes seen on rotting wood or in tan 

 pits, may measure several centimeters in breadth. 



FIG. 44. A mce ba vespertilio. (After Doflein.) 



Like all living things, the protozoa are composed of protoplasm. 

 Protoplasm is a complicated and, more or less, fluid mixture of albuminous 

 substances. A cell may be conceived of as a tiny drop of albuminous 

 and somewhat viscid fluid, like the white of an egg. By appropriate 

 methods, the protoplasm of a cell may be shown to have an alveolar or 

 foam-like structure; because the protoplasm is a mixture of two fluids, 



