18 



NATURAL HISTORY 



Animals also differ with different types of soil. This is particularly 

 true of the bottoms of lakes or streams. A different fauna is found 

 on the rocky stream bed from the soft mud of the pool below. Mud 

 contains more food, but it is also more difficult for organisms living 

 in it to carry on respiration. Soil is also the home of such burrowing 

 animals as nematode worms, earthworms, ants, beetles, digger wasps, 

 and the larvae of various insects. 



Molar Agencies 



Such are any moving agencies. Running water and winds erode ; 

 ice moves soil and rocks. Tides cause great differences in aggrega- 

 tions of plant and animal life, animals living between tides having 

 different problems to face from those below the tidal flow. Moving 

 air has a definite effect on vegetation, as is often seen in the wind- 

 blown trees on mountainsides or plains. Moving air acts upon seeds, 

 tumbleweeds, spores, and fruits, thus spreading plants over vast 



American Museum uf Xatural History 



Tidal shores, along the New England coast, show wide variations in habitat. 

 The flora and fauna of the intertidal zone differs greatly from that of the regions 

 above and below the tidal flow. 



