ACTIVITY OF HABITS. 19 



this insatiable, though miniature army, provided 

 for the purpose. They, in their turn, afford 

 sustenance to aquatic insects, which are again 

 preyed on by fishes ; and thus food is prepared 

 for more highly organized animals, and lastly 

 for man. 



Animalcules have never been observed to rest, or 

 at least to sleep ; but this may be partly owing to 

 the light necessarily used in viewing them, which 

 forms an artificial sun -light, exciting their powers 

 of motion : they may rest during darkness, when 

 they cannot be seen by us. Many are only at- 

 tracted to the surface of the water by the light 

 of the sun, and are difficult to be obtained on a 

 dull day ; they are, however, not much affected 

 by cold or heat, for they are procurable in winter 



