PROTOZOA 163 



that manufacture their own food. Some Kve on debris, some 

 are predatory, some are parasitic, and some are symbiotic with 

 alg£e. Rhizopod shells dropping to the bottom of the ocean 

 form the "ooze," — the chalk of later geological epochs. Other 

 forms of limestone also are produced by the accumulations of 

 these 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 animals. Malaria and 

 yellow fever in man are caused by Sporozoa and Mastigophora 

 respectively, in the blood. In both these diseases, species of 

 mosquitoes are the cause of the introduction of the parasites 

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

 of the diseases of cattle, is communicated through the cattle 

 tick, in which the sporozoan producing the disease undergoes a 

 portion of its life history. Trypanosomes, flagellate blood- 

 parasites, are responsible for "sleeping sickness" in man in 

 tropical regions. Similar parasites are found in the blood of 

 rats and other animals. 



Amoeba-like rhizopods in the intestine of man cause some 

 forms of dysentery and other derangements of the tract. Sim- 

 ilar organisms have been supposed to cause pyorrhea. Certain 

 problematical organisms accompany small-pox, hydrophobia, 

 and other diseases, though it is not known whether they have 

 an active influence on the diseases. 



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. 



203. Supplementary Studies for the Library. 



I. The reactions of Protozoa to light; to chemical substances; to heat; etc. 



