ACTION OF THE CABNITOEOUS WATER-BEJBTLES. 177 



emitted by the specimen when under water. The same afternoon 

 this specimen, at 3.19, was observed to be suspended at the surface 

 of the water in an absolutely motionless condition, in which condi- 

 tion it continued till 3.59. Owing to its position, it was not for 

 certain ascertained whether any crack for breathing remained open 

 or not. At 3.59 it moved, and the aperture under the elytra was 

 widely opened ; and at 3.60 it descended, but speedily came up 

 again and resumed its former motionless position at the surface, 

 which it retained for nearly half an hour ; during this half-hour 

 its position was such that it could be observed with a magnifying 

 lens ; this was done several times, and a small breathing-aperture 

 was always observed to be present. 



Only a single observation was made on this species, and during 

 that observation the insect was feeding. This beetle remained 

 for long periods suspended at the surface of the water : it was 

 in this exposed position on one occasion for 40 minutes without 

 moving. 



XIII. Agabus bipustulatus. 



No. 1. Aug. 26th, 1875. — A female specimen observed from 

 1.51 P.M. till 2.31 P.M. Between these times it rose for purposes 

 of aeration at 



1.54, remaining up 8 sees. 

 2. 6 „ 55 ., 



2.18, remaining up 8 sees. 

 2.25 „ 35 „ 



No. 2. Sept. 5th. — The same insect again kept close scrutiny 

 upon ; and the accompanying notes show the intervals of its 

 appearance at the surface : — 



3.22, observation commenced. 

 3.24, remained up 45 sees. 

 3.35 „ 30 „ 



3.43 „ 12 „ 



3.55 „ 21 „ 



4. 6 „ 10 „ 



4.21, remained up 65 sees. 

 4.34 „ 22 „ 



4.38 „ 17 „ 



4.47 „ 37 „ 



5. 1 „ 15 „ 



5. 2, observation ceased. 



The insect buried itself in the mud so that it could not be 

 seen ; this it only left for breathing, and descended immedi- 

 ately, except in the case of the small interval 4.34-4.38, when 

 it moved about the bottom instead of concealing itself. The 

 elytra are held very wide open for breathing. 



