8i6 General Notes. [_October, 



during mild winters both summer and winter ^^%?> are produced, 

 and the successive broods of young after producing agamic 

 young, throw off an ephippium so that the pool is filled with eggs 

 which are calculated to stand any vicissitude. Thus it happens 

 that after a pond has been dried for a long time the first warm 

 shower quickens in it swarming life. The above facts are more 

 significant when we remember that the Cladocera are above all 

 others among Crustacea, the most useful as purifying agencies. 

 The greater number subsist entirely upon vegetable matter, and 

 the only means they have of collecting it is by causing a current 

 of water containing such minute particles as may exist in it to 

 pass between the rotating jaws, though, perhaps, in some cases the 

 labrum is sufficiently prehensile to grasp somewhat larger food. 

 Certain it is, however, that these same minute animals form an 

 indispensable agent in the economy of nature, purifying all our 

 stagnant pools of the decaying vegetation floating therein. One 

 who had given no attention to the number of these creatures 

 would undoubtedly be surprised on carefully examining a given 

 quantity of water from the nearest lake. Here are some figures. 

 In a quart of water taken by dipping from a lake near Minne- 

 apolis, the following were counted : 



Ceriodaphnia 1400 



Daphnia 9 



Simocephalus 56 



Cypris 50 



Cyclops 28 



Amphipods (chiefly young) 120 



Infusoria 35 



Mollusks 22 



Diptera (larvae) 100 



Hemiptera , 9 



etc., all visible to the unassisted eye. — C. L, Herrick. 



