200 ELEMENTARY LESSONS ON INSECTS 



glass having its lower edge sunk in the soil of the pot, and 

 a cheese-cloth cover. 



Small transparent insects, for examination with the micro- 

 scope. — These may be obtained from any weedy, permanent 

 pond, by lifting some of the floating "pond scums" and trash 

 with a small dip net and placing it in shallow white dishes 

 in clean water. Damselfly and mayfly nymphs will quickly 

 appear (along with water fleas and other 

 minute aquatic animals) swimming around 

 the edges of the dish. The damselfly 

 nymphs will be recognized by the three 

 flat, vertically placed platelike tracheal 

 gills in which the body terminates; the 

 mayfly nymph, by the paired gills on the 

 back of the abdomen, one pair on each of 

 the first seven segments. Midge larvae 

 will also probably appear: minute worm- 

 like creatures that swim jerkily, by means 

 of figure-of-8 loopings of the body. Either 

 will show what is wanted for this study. 



Choose the smallest and most transparent specimens to 

 place under the microscope. Put them in hollow ground slides, 

 or support the coverglass over them to avoid crushing. Use 

 only living specimens. 



Fig. 72. — A lantern-globe 

 live cage. 



