How they perform the primary functions 



Fig. 23. The aquatic nymph of a may-fly, with leaf-Hke tracheal gills along 



the sides of the abdomen. The three long filaments at the tip of the 



abdomen are not gills, but act as organs of balance 



Water-beetles, and water-bugs, when they dive below the surface, 

 take down with them a bubble of air which is held in contact with their 

 open spiracles by a cluster of hydrofuge (water-repelling) hairs. Because 

 these hairs are not wetted the bubble is held trapped, and it serves as 



39 



