joo Descriptive Zoology. 



Distribution of Protozoa. All protozoans are aquatic, 

 though some might seem to be exceptions, living as they 

 do in damp moss ; but they are probably in thin films of 

 water on the surface. Protozoans are the most widely 

 distributed of animals, occurring almost all over the globe, 

 in fresh water and in the ocean, in lakes and rivers, ponds 

 and creeks, pools and ditches. In the ocean they are 

 more abundant in shallow water, but are also found at 

 considerable depths and at the surface of the deeper seas. 



The Importance of Protozoa. Protozoans are highly 

 important in two respects : ( i ) they have contributed 

 much to rock-making, and are still making deposits on the 

 ocean bottom ; (2) as a source of food to the animals of 

 the ocean, it is difficult to overestimate their importance. 

 In countless myriads they serve as food for animals som< 

 what larger and higher in the scale than themselves. 

 These animals, in turn, are the food for still higher animals. 

 The protozoans, then (with the protophytes or one-celled 

 plants), may truly be said to be the food foundation of all 

 the higher marine animals. 



PROTOZOA AND METAZOA. 



Protoplasm. Protoplasm is the living substance of 

 animals and plants. It is a clear, jellylike substance, 

 which does not dissolve in water nor readily mix with it. 

 When seen in water its outlines are usually quite distinct. 

 It may appear more or less dotted on account of various 

 kinds of matter suspended in it. An amoeba is a mass 

 of protoplasm, and the properties of protoplasm were con- 

 sidered in connection with amoeba. Protoplasm has the 

 power of movement, is capable of being stimulated, i.e. is 

 irritable, it eats, grows, breathes, throws off waste matter, 

 or excretes, and has the power of reproduction. 



