358 Annals Entomological Society of America [Vol. IX, 



evidence is yet at hand to definitely indicate the purpose of 

 these peculiar structures, but in view of the absence of storage 

 reservoirs for air and of the bug's proneness to submerge itself 

 for long periods of time, it is not unreasonable to surmise that 

 dissolved air is extracted from the water, thus aerating the body 

 fluids as they flow by within the body cavity. The other 

 functional spiracles are the thoracic, which are large and 

 well- developed and apparently used when the insect is in flight, 

 as they are exposed by bending the thorax forward when 

 Ranatra, for instance, takes to the air. In the nymph, the 

 respiratory device is superficially the same as in the adult, 

 but is actually quite different. Here all the abdominal spiracles 

 are functional and air is led to them by a very short tube. 

 This is formed by the folding over of the produced last abdom- 

 inal segment, the amplified connexivum of the others being 

 bent over to form a channel over the spiracles, which are thus 

 in direct contact with air. The internal organization of the 

 respiratory system in nymphs has not as yet been investigated. 

 The third type of respiratory devices, that is, the abdominal 

 channel, has been but little studied. It is, however, extremely 

 simple. The abdomen is keeled down the middle and from 

 this keel spring outwardly toward the sides of the body elastic 

 and fairly stifT and close-growing long hairs, which meet similar 

 hairs arising from the connexivum edge. There is thus formed 

 a channel on each side of the abdomen which is filled with air 

 and in which the spiracles are placed. The bugs hang in the 

 water abdomen up with its extremity just piercing the surface 

 film. In most species there are three tufts of hair which spread 

 out on the surface leaving an open, water-free spot in the middle 

 which is the point where the connection is made between the 

 abdominal reservoirs and the atmosphere. When totally 

 submerged, the opening closes in some way not well explained 

 so far, although the writer believes that the three tufts mentioned 

 lap over and in some manner serve to obstruct the entrance 

 of water into the channels. In any case, these channels act 

 as storage reservoirs while the insect is in its element. The 

 hairs are not set so near together as to touch, but they are 

 sufficiently close to form an aqueous film at a tension between 

 them which acts to retain the air in the chambers and at the 

 same time to keep water out. This is very necessary in many 

 species, as they only come to the surface to renovate their 



