l62 ZOOLOGY 



them important. Together with bacteria they serve to save 

 for the organic world much decaying material which no other 

 animals could utilize. The bacteria decompose organic matter 

 and the protozoa devour bacteria. They in turn become food 

 for higher animals. We have seen that there are green forms 

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

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

 algae. 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 

 possibly yellow fever in man are caused by Sporozoa 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. Trypanosomes, flagel- 

 late 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. Similar 

 organisms accompany small-pox, hydrophobia, pyrea, and 

 other disease, 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 



