2-10 THE CANADIAN ENTOMOLOGIST. 



possibly to fill the large air-chambers that are found in the thorax of 

 Ranatra, when the head is bent forward at the moment of taking flight, 

 as previously described. 



The respiration of the adult while in the water is evidently through 

 the air-tube or siphon. This may also be used when out .of the water, 

 but the main reliance is probably in the thoracic spiracles in the latter 

 case. The great disparity in size of the latter as compared to the former 

 is in all likelihood due to the violent exertions Ranatra makes while in 

 the air in flight, these, so far as known, being the only occasions on which 

 it leaves its natural element. Of course, while in its customary surround- 

 ings, its sluggish habits make deep breathing unnecessary, and, as 

 suggested before, the so.called false stigmata may be functional in some 

 way when the bug is submerged. 



The air-tube, as Marshall and Sjveiin point out,'^ may be cut off 

 short without causing the insect any apparent inconvenience. This, of 

 course, has further proof in the varying lengths of the tube in different 

 individuals of the same species, in different species, and in different 

 genera. What is more remarkable, is that a difference in length between 

 the two halves of the tube seems not to affect its usefulness. Among my 

 captures was a Ranatra in which one-half of the siphon was broken off 

 withm an eighth of an inch from the body, and which lived for some 

 months in my aquarium. When entering the water after being out of it 

 for any length of time, the two halves of the air-tube are moved 

 alternately in and out. Sometimes the silvery column of air can be seen 

 rising in it little by little, from the abdomen, till at length it reaches the 

 distal end of the siphon. MialP* claims that in R. linearis the continuity 

 of the tube "is maintained by a multitude of hook like bristles, which 

 project from the opposed edges." This is not the case in Ranatra 

 guadridentata, in which these fringing hairs are simple. Indeed, the 

 fact that the bug can separate the halves at will as well as move them 

 independently of each other, would seem to militate against this view. 

 Further, the natural formation of a surface film where water is in contact 

 with air in limited areas, would render such a device unnecessary. 



In the nymph the respiratory system is very different from that of the 

 adult. The principle, of course, is the same in both, since both breathe 

 atmospheric air which they get by piercing the surface film by means of a 



13. Op. c, p. 494. 



14. Natural History of Aquatic Insects, p. 353. 



