Aquatic Adaptations of Insects 275 



of the hind legs, and thence it goes through a transverse 

 groove-like passage (fig. 168) to a chamber underneath 

 the wing bases, where there are two enlarged spiracles 

 on each side. The beetles of the family Hydrophilidffi 

 have their ventral surface covered with a layer of fine 

 water-repellant pubescence, to wliich the air readily 

 adheres. Thus the air is carried exposed upon the 

 surface, where it shines like a breastplate of silver. 



In the waterbugs, the air is usually carried on the 

 back under the wings, but the inverted back-swimmers 

 conduct air to their spiracles through longitudinal 



Fig. 168. Diagram of the air- taking apparatus of the beetle, 

 HaUplus. The arrow indicates the transverse groove that 

 leads to the air chamber. (From Matheson). 



grooves that are covered by water-repellant hairs, and 

 that extend forward from the tip of the abdomen upon 

 the ventral side. The water walking-stick, Ranatra, 

 and some of its aUies have developed a long respiratory 

 tube out of a pair of approximated grooved caudal 

 stylets. This long tail-like tube reaches the surface 

 while the bug stays down below, breathing like a man 

 in a diving bell. 



The immature stages of aquatic insects are far more 

 completely adapted to life in the water than are the 

 adults. Some members of nearly all the orders, and all 



