A GUIDE TO THE STUDY OF BRITISH WATERBUGS. 115 



delicate matter. The body is tilted up on one side by means of 

 the anterior pairs of legs and one posterior leg ; the other pos- 

 terior leg (that on the uptilted side) performing the work. 



Hydroessa does not, I think, move very far out from the water's 

 edge, and scuttles in under the shelter of the bank upon being 

 disturbed. 



One specimen (macropterous) appeared to have been drowned ; 

 — on removing it from the water it remained perfectly motion- 

 less. I then placed it upon its back for the purpose of examining 

 the ventral surface ; after a few moments, first one of the legs, 

 and then another — finally five and one antenna — began to pul- 

 sate feebly but rhythmically. The bug appeared to be quite 

 dead, but the pulsations nevertheless accelerated (unequally in 

 the different legs) and increased in vigour. Upon tapping the 

 support, the movements ceased, but recommenced after a short 

 interval. Unfortunately, an accident prevented more extended 

 observations. These pulsations are well known to occur in the 

 Ehynchota,* and are quite distinct from the ordinary muscular 

 movements. 



Explanations of Plate I. 



FIG. 



1. Velia rivuloritm (Fabr.) ; head, pronotum, &c, of apterous form. 



2. Head, &c, of rnacropterous form of same species. 



3. Sterna of same species. 



4. Anterior tarsus, same species. 



5. ,, ,, Hydrometra stagnorum (Linn.). 



6. Mesovelia f areata Muls. & Rey, $ , apterous form (dorsal view). 



7. Antenna of Gerris najas (De Greer), Kirk. 



8. ,, G. rufoscutellatus, Latr. 



9. ,, G. lacustris (Linn.), Stal. 



10. Head and antenna (dorsal view) of Hydrometra stagnorum (Linn.). 



11. Sterna of Gerris najas (De Geer), Kirk. 



12. Apical segments of abdomen (ventral view) of Hydroessa pygmaea 



(Duf.) $. 



13. Apical segments of abdomen (ventral view) of Hydroessa pygmaea 



_ (Duf.) ? . 



14. Apical segments of abdomen (ventral view) of Velia rivulorum 



(Fabr.) $. 



a. pronotum, b. mesonotum, c. metanotum, d. first segment of abdomen, 

 e. prosternum, /. mesosternum, g. metasternum. 



* See W. A. Locy — " Observations on the pulsating organs in the legs of 

 certain Hemiptera " — (Amer. Nat., 1884, pp. 13-9, Plate i.). 



(To be continued.) 



