68 



ANIMAL LIFE AND SOCIAL GROWTH 



the surrounding medium. The monads are also 

 the first organisms to decHne in numbers and 

 practically to disappear. Their decrease is prob- 

 ably due in part to the rapid decline in numbers 

 of the bacteria present as fed upon by the monads 



Fig. 3. Monads. 



Fig. 4. Colpoda. 



and to the rising generation of Colpoda (Fig. 4). 

 The fact that they appear at a time of high acidity 

 is probably incidental. 



Infusorians known as Colpoda are the second 

 organisms to appear in numbers. In the series 

 we are following they are present in maximum 



