FIELD BOOK OF PONDS AND STREAMS 



are the only plant growths. The animals stay on the under 

 surfaces of the stones, hiding beneath them, or on their lee 

 sides. Among them are a few small fishes — darters and 

 minnows — two-lined salamanders, flattened mayfly and stone- 

 fly nymphs, net-building caddis fly larvse, "water pennies," 

 Simulium larvae, leeches, planarians, and the swift-water 

 snails — Ancylus and Goniohasis. 



Work upstream. Pull stones from the water, turning them 

 over quickly before the stonefly nymphs drop off; examine 

 them carefully, since many of the animals cling tightly and 

 are the same color as the stone. Hold the net against the 

 current, stirring up the stones and gravel above it so that the 

 animals which are dislodged will be caught in it. 



Waterfalls. — Water mosses, Hygrohypnum and Fontinalis, 

 are apt to grow here and clambering animals hide among 

 them — larvae of caddis flies and the cranefly Dicranomyia, 

 crustaceans lilce Gammarus and Asellus, small mayfly nymphs 

 and many midge larvae. 



Clear pools, — In gently flowing streams, usually in their 

 clear pools, are beds of little white mussels of the genus 

 Splicer ium. Asellus is common in tiiem and nymphs of the 

 dragonfly, Cordulegaster. 



Leaf -harriers. — Leaves and trash catch in the riffles form- 

 ing leaf-barriers which hold their own distinct societies 

 wherein the crustaceans — Asellus and Gammarus — are prom- 

 inent, and the largest of the cranefly larvae, Tipula ahdomina- 

 lis. 



Springs. — Green algae spread over spring pools and form 

 "blanket algae" communities (p. 50). These are populated 

 by minute forms — diatoms, desmids, protozoans, worms, 

 rotifers, crustaceans, and midge larvae. 



On land, hy ponds and streams. — IMany kinds of animals 

 leave the water but stay in the regions near it. Frogs forage 

 among the grasses, along the banks; salamanders hide beneath 

 stones on the wet shores or in drier places nearby. Adults 



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