POND LIFE. 137 



cality where there are ponds of water, and they are 

 very easily kept in aquaria. 



1. Remove a few specimens from the aquarium, 

 and place them in a glass of water in the bottom of 

 which there is a layer of gravel 



or small pebbles. If several 

 specimens are placed in the 

 glass, some of them may come to 

 rest near enough the side of the 

 glass so that they may be studied 

 with a lens. 



2. Note that the favorite at- p,^ 

 titude of a water-boatman is 



clinging to a pebble at the bottom of the aquarium 

 by the tips of the middle legs, with the fore legs 

 bent up under the head and the hind legs stretched 

 out sidewise like oars. This is a very different at- 

 titude from that assumed by their near relatives, 

 the back-swimmers. 



3. Note that there is a thick layer of air covering 

 the entire belly or ventral side- of the body. Some- 

 times this layer of air extends down the legs nearly 

 or quite to the ends of the coxas, and often there is a 

 strip of air on the outside of the outer edge of each 

 upper wing. The spaces between the head and pro- 

 thorax, the prothorax and mesothorax, and between 

 the wings and abdomen are also filled with air. These 

 masses of air can be seen when the insect bends its 

 body. 



4. By watching these insects carefully, you will 

 be able to see that sometimes one will lift its wings 

 slightly, thus drawing the air from the ventral side 

 of the body up under the wings ; and, on the other 



