31^ 



Aquatic Societies 



coid green alga:. The herbivores are such short-lived 

 crustaceans as Chirocephalus (see fig. 90 on p. 184) and 

 Apus, which have long-keeping, drouth-resisting eggs; 

 such rotifers as Philodina, remarkable for its capacity for 

 resumption of activity after dessication ; such insects as 

 mosquitoes. The carnivores are such adult water-bugs 

 and beetles as may chance to fly into them. 



Whether a population shall be able to maintain itself 

 depends on the continuance of favorable conditions, at 

 least through the period of activit}^ of its members. 

 In these pages we shall give attention only to the life 

 of relatively permanent waters. 



Plants — The shoreward distribution of plants in 

 natural associations is determined mainly by two 

 hydrographic factors: (i) movement and (2) depth of 

 the water. It is directty related to exposiore to waves 

 and to currents. Everyone knows the difference in 

 appearance between plants growing immersed in a quiet 



Flij. lbs. The forefront of the Canoga marshes, where partly sheltereJ 

 from the waves of Cayuga Lake, clumps of the lake bulrush lead the 

 aflvance of the shore vegetation. 



