ECHOES OF BATS AND MEN 



which is covered well in the Science Study Series book 

 Soap Bubbles, 



More pertinent is the fact that the water beetles make 

 use of surface waves to keep themselves posted about 

 the proximity of the water's edge. They have eyes and 

 use them under many conditions, but at night or when 

 vision is prevented by laboratory experiments performed 

 in darkness they still manage quite skillfully to avoid 

 collisions with the edge of an aquarium and with each 

 other. A German biologist named Friedrich Eggers 



Fig. 5. A whirligig beetle whose other legs lie beneath 

 its body is able to sense water waves and their echoes 

 with the two specialized antennae which protrude from 

 the head and float on the water. It is also interesting 

 to note that this beetle has four compound eyes, two 

 above the water and two below. 



Studied these beetles with great care in the 1920s. Un- 

 like those of most insects, their antennae, or feelers are 

 shaped in an especially suitable way to float on the sur- 

 face film of the water. The numerous hairs all arranged 



54 



