FIELD BOOK OF PONDS AND STREAMS 



Collect with a water-net, sweeping it through the water 

 and brushing the submerged vegetation. Turn the lily pads 

 for snails, sponges, bryozoans, and insect eggs. Almost any 

 of the plants harbor snails and little crustaceans. 



Fig. 31. — Collecting with a plankton-net: i, skim- 

 ming the surface; 2, draining off the extra water; 3, 

 pouring plankton out of the net; 4, plankton organ- ' 

 isms after settling. 



In the surface water. — In the open surface water of ponds 

 and lakes are the plankton or microscopic plants and animals 

 — desmids, diatoms, blue-green algas, protozoans, crustaceans 

 adult and young, and rotifers (PI. IV). 



To collect plankton near shore or in the smaller ponds 

 skim the surface with a long-handled, cone-shaped, plankton- 

 net made of silk bolting cloth, trailing the net through the 

 water (Fig. 31,1) preferably from a boat. After a few minutes' 

 continuous skimming, let the net drain until only a cup or 

 so of water remains, then loose the string letting this through 

 the open end (Fig. 31, 3). Such skimming should be repeat- 



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