Economic Importance of Animals 535 



produces the silkworm disease (pebrine) ; Pseudospora volvocis is a para- 

 site on another protozoan animal, l^olvox. 



Certain flagellated Protozoa (class, Mastigophora) live symbiotically 

 in the intestines of wood-feeding termites ("white ants"). The Protozoa 

 receive protection, in turn digesting the woody materials for use by the 

 termites. Enzymes produced in the bodies of the Protozoa make the wood 

 particles in the intestine of the termites available for the latter. The 

 mutual benefit is classed as a case of symbiosis. Cristispira (class Mas- 

 tigophora) frequently is found in oysters and clams. Certain ciliated 

 Protozoa (class Infusoria) destroy bacteria in sewage disposal plants. 

 This phenomenon is taken advantage of in the necessary destruction of 

 sewage. 



Certain types of Protozoa, especially in water, furnish foods for other 

 animals. Protozoa are well adapted for laboratory experimentation for 

 such studies of life processes, characteristics of living protoplasm, cell 

 studies, and the efTects of physical and chemical agents on living proto- 

 plasm, as well as many others. Many Protozoa are at present unknown, 

 and many of those which have been studied are of unproved economic 

 importance. Undoubtedly, future work will place many more in their 

 proper places in the economies of Nature. 



PHYLUM 2— PORIFERA (SPONGES) 



Sponges furnish protection for both plant and animal organisms. They 

 are not used as foods because of the presence of skeletal spicules, strong 

 odors and tastes, poisonous ferments, and an extremely small amount of 

 stored food material in their bodies. Boring sponges (Cliona) bore the 

 shells of oysters and other mollusks for protection rather than for food. 

 The siliceous sponges and certain Protozoa (order Radiolaria) initiate 

 the process of flint formation. It is stated that beds of flint may be made 

 from a mass of sponge skeletons within fifty years. 



Fresh-water sponges (Fig. 86) frequently attach themselves to water 

 pipes, reservoirs, water filtration equipment, and, together with other 

 miscellaneous forms of life, form a feltlike mass which interferes with the 

 water system. 



Sponges may starve oysters and other shelled mollusks by attaching 

 themselves to the shells and taking the food from the mollusks, and they 

 may interfere with other forms of life in their vicinity by using the oxygen 

 in the water. 



