ACTION OF THE CAENIYOKOUS "WATER-BEETLES. 



165 



neously. At 9. 14 and again at 9.28 it acted in a similar way, 

 while at 9.42 1 myself stopped short observing. The whole ope- 

 ration of rising, opening elytra at surface, diving and burying 

 itself again in the mud was performed ia each case with such 

 rapidity as to yield merely sufficient time for its recognition. 



No. 7. Oct. I7th. — This observation, on a female, commenced 

 at 2.1 P.M. It then lay concealed in the mud, but rose at 2.18, 

 resting for about 2 seconds for the purpose of aeration. My 

 observation ceased at 3.4 p.m. 



No. 8. Eenewed observation at 4.25 p.m., and kept watch until 

 5.25. During this hour the beetle remained concealed in the 

 mud and was not visible. 



No. 9. Same night at 9.7, by lamplight. — The insect was con- 

 cealed in the mud and did not rise whilst notice was kept, viz. 

 until 10.7 P.M. 



The following tabular statement gives the numerical results 

 of the foregoing series of observations. 



Summary. — From what has been stated, it may be inferred 

 that Pelohius Mermanni rises for the purpose of aeration on the 

 average once in every 21 1 minutes, but often goes one hour 

 without ascending to the air. In these observations the time it 

 remained at the surface to perform aeration or respiration varied 

 from a single second, or less, to 20 seconds, and was, on the ave- 

 rage, 5 seconds ; and the time it was exposed bore to the time it 

 was concealed a ratio of 1 : 375. The observations also suggest 



