1916] Aquatic Hemiptera 359 



air supply, remaining at some distance below the surface the 

 greater part of the time. Very little seems to be known in 

 regard to their internal respiratory system. It might seem, 

 though, that it should be simple. The nymphs are not different 

 from the adults in this adaptation. 



All these devices, as can be readily understood, are nicely 

 correlated to the varying conditions under which the groups 

 live. The forms with the pile and reservoir type are deep- 

 water dwellers, the Corixidce. clinging to the bottom, the Bel- 

 ostomatidcE hiding among the rubbish and mud, the NaucoridcB, 

 in a general way, living in the subaquatic vegetation. All 

 comparatively seldom come to the surface; all, therefore, 

 need some means of obtaining air while under water, which will 

 provide a way for its constant automatic renovation independent 

 of direct contact with the atmosphere except at comparatively 

 long intervals. And here we have it. The air and oxygen 

 contained in the water in some way seem to purify the air 

 enmeshed in the pile by contact or by solution and absorption 

 of its contained impurities. In the NepidcE, the difficulty to 

 respiration arising from long submergence is obviated by the 

 so-called false spiracles which, in my view, act as gills and 

 directly aerate the body fluids, which is another most striking 

 adaptation to a special environment. The Notonectidce have 

 no remarkable peculiarity in this respect, as all come to the 

 surface at comparatively short intervals. 



In all the aquatic and semi-aquatic forms, predatory habit 

 is the rule, and accordingly the front pair of legs is modified 

 into powerful prehensile organs, excepting only the CorixidcE, 

 of which more later. The other two pairs of legs are adapted 

 in the purely aquatic section, in a greater or less degree to 

 swimming, some being highly specialized and others scarcely 

 so. In the majority of the Belostomatida, the hind pair of 

 legs is broadened to a very marked degree, especially the tibiae, 

 which are heavily fringed with long hairs. These are exclu- 

 sively used in locomotion under water. Lethocerus americanus, 

 for instance, when hard pressed and with a free field, stretches 

 out its raptorial front legs before it, and gives long strong 

 propulsive strokes with the other two pairs moved synchro- 

 nously. This is true also of our other native forms of the 

 family, although, since the middle legs are neither so broad nor 

 so powerful, the brunt of the labor is borne by the hind pair in 



