HOW INSECTS BREATHE 



137 



break through the surface film of the water and 

 are supposed to aid in supplying fresh air to the 

 tiger's respiratory system. The water-tiger has to 

 pull manfully to get his tail under water again. 

 You may see him beat his great hairy legs against 



WATER-TIGERS 



the water in order to get under way and then 

 dart down like a. trained diver. 



Another frequent visitor to the surface is the 

 back-swimmer. Like the water-tiger it often hangs 

 head downward, with the tip of the body at the 

 surface. We suspected it of getting its air in the 

 same fashion. But the entomologist showed me 

 that this was not true. We took a back-swimmer 

 from the water and placed it in its favorite posi- 

 tion with the wings downward. On the surface 

 of the body now uppermost we found a distinct 



