382 CHRISTINE ESSENBERG 



to the air. When in this position the fore- and middle-legs are 

 slightly bent so that the claws are at the surface. The insects 

 often rest at the bottom, clinging to sticks or weeds. 



It is also interesting to note that the hairs of the body are 

 so arranged as to facilitate respiration. On the forelegs are 

 two rows of hairs pointing in opposite directions, and partly 

 covering the spiracles on the thorax. The ventral surface of 

 the thorax has a double row of thick hairs on both sides of the 

 margin, pointing posteriorly and meeting the hairs of the abdo- 

 men. There is also a double row of hairs on each lateral margin 

 of the abdomen; the hairs of the outer rows increase in length 

 as they approach the posterior end of the abdomen, where they 

 end in one row of long tufts. The inner rows of marginal hairs 

 cover the pleura and can be napped back by the contraction of 

 the abdomen. The carina or the ventral midpart of the abdo- 

 men is thickly covered with hairs which extend laterally on both 

 sides and overlap the hairs from the lateral margin, which 

 extend toward the middle line. Thus the rows of hairs form a 

 waterproof covering over the gutters which he one on each side 

 of the carina and serve for the conveyance of air. In addition 

 to the rows of long hairs described, the whole surface of the 

 abdomen is covered with short hairs. On the dorsal surface, 

 beneath the wings, there is a row of hairs between each segment, 

 pointing posteriorly, while fine hairs cover the entire dorsal 

 surface of the abdomen. The hairs are covered with an oily 

 secretion which prevents their getting wet. 



Three pairs of spiracles are found on the thorax, and a pair 

 on each segment of the abdomen in the pleura. The air finds 

 entrance to the spiracles from the posterior end of the body, 

 where an opening is formed by the tufts of hairs as soon as the 

 animal reaches the surface of the water. The hairs cling together 

 and close the opening as soon as the animal is submerged. Some- 

 times the whole fringe is lifted like a lid from the pleura when 

 the animal reaches the surface of the water, closing again as soon 

 as it sinks. The bug comes to the surface to receive a fresh sup- 

 ply of oxygen and to emit carbon dioxide. The bug being sur- 

 rounded by air, is lighter than the water so that it is compelled 

 to keep the rowing legs in constant motion in order to keep 

 beneath the surface. As soon as the leg-motion ceases, the air 

 buoys the insect up until it meets the surface film. As soon as 



