188 THE RELATIONS OF PLANTS TO ANIMALS 



lives within the shell of the oyster ; the sea anemones, which are 

 carried around on the backs of some hermit crabs, aiding the 

 crab in protecting it from its enemies, and being carried about 

 by the crab to places where food is plentiful. 

 * A Hay Infusion. Still another example of the close relation 

 between plants and animals may be seen in the study of a hay 



Life in a late stage of a hay infusion. B, bacteria, swimming or forming masses 

 of food upon which the one-celled animals, the paramoecia, are feeding ; G, 

 gullet; F.V., food vacuole ; C.V., contractile vacuole ; P, pleuococcus ; P.D., 

 pleurococcus dividing. 



infusion. If we place a wisp of hay or straw in a small glass jar 

 nearly full of water, and leave it for a few days in a warm room, 

 certain changes are seen to take place in the contents of the jar; 

 the water after a little while gets cloudy and darker in color, and a 

 scum appears on the surface. If some of this scum is examined 

 under the compound microscope, it will be found to consist almost 

 entirely of bacteria. These bacteria evidently aid in the decay 

 which (as the unpleasant odor from the jar testifies) is taking place. 

 As we have learned, bacteria flourish wherever the food supply is 



