PROTOZOA. 155 



calcareous shells. Similar masses of the siliceous shells occur 

 in various parts of the earth. Some of the Protozoa, especially 

 the parasitic Sporozoa produce diseases in man and other ani- 

 mals. Malaria and yellow fever in man are caused by Sporo- 

 zoa in the blood. In both these diseases, species of mosquitoes 

 are apparently the cause of the introduction of the spores into 

 the human system. Texas fever, one of the most dreaded of 

 the diseases of cattle, is believed to be communicated through 

 the cattle tick, in which the sporozoan producing the disease 

 undergoes a portion of its life history. 



Pieces of such protozoa as Stentor have been shown to be 

 able to regenerate a whole animal, provided a portion of both 

 nucleus and protoplasm are present, but not otherwise. This 

 shows that each is necessary to the activities of the animal. 

 Because they are lowly and simple animals, we must not con- 

 sider that they are either unimportant or unsuccessful in the 

 struggle for existence. Their wonderful reproductive power 

 insures that they hold their own whenever the conditions are 

 at all favorable for them. They occur in practically all the 

 waters of the earth, increasing or decreasing as their food 

 varies in abundance. 



198. Supplementary Studies for the Library. 



1. The reactions of Protozoa to light; to chemical substances; to heat; 

 etc. 



2. Their power of resistance to heat ; cold ; drouth. The practical 

 results thereof. 



3. The economic importance of Protozoa. 



4. What is "plankton"? What is the importance of its study? 



5. Conjugation in Protozoa. Compare methods of reproduction and 

 conjugation in the various groups. Follow the nuclear changes in con- 

 jugation of Paramecium. 



6. Why should Volvox and Euglena be considered animals rather than 

 plants ? 



7. Diseases in man or animals believed to be caused by the sporozoa. 

 The role of the mosquito in the life history of the sporozoa causing ma- 

 laria and yellow fever. The bearing of these facts upon infection and the 

 management of these diseases. 



8. Forms of the Protozoa of different classes as shown by the illustra- 

 tions in the larger text-books. 



9. The varying form of the nucleus in different species of Protozoa. 



