THE RELATIONS OF PLANTS TO ANIMALS 165 



life. In the water, too, there may have been some living cells, 

 plants and animals. 



At first the multiplication of the tiny animals within the hay 

 infusion is extremely rapid ; there is food in abundance and near 

 at hand. After a few days more, however, several kinds of one- 

 celled animals may appear, some of which prey upon others. Con- 

 sequently a struggle for life takes place, which becomes more and 

 more intense as the food from the hay is used up. Eventually 

 the end comes for all the animals unless some green plants obtain 

 a foothold within the jar. If such a thing happens, food will be 

 manufactured within their bodies, a new food supply arises for the 

 animals within the jar, and a balance of life may result. 



REFERENCE BOOKS 



ELEMENTARY 



Hunter, Laboratory Problems in Civic Biology. American Book Company. 

 Sharpe, A Laboratory Manual for the Solution of Problems in Biology, pp. 133-138. 

 American Book Company. 



ADVANCED 



Eggerlin and Ehrenberg, The Fresh Water Aquarium and its Inhabitants, Henry 



Holt and Company. 



Furneaux, Life in Ponds and Streams. Longmans, Green, and Company. 

 Parker, Biology. The Macmillan Company. 

 Sedgwick and Wilson, Biology. Henry Holt and Company. 





