ACTION OP IHK CAENIVOROirS WATEB-BEETLES. l75 



faster motion is performed by moving the hind tarsi rapidly (or 

 perhaps the hind tarsi and tibiae), while the femora are kept flexed 

 on the breast. This motion may be at once changed into a 

 rapid violent shoot forwards, caused no doubt by the femora and 

 the ^rhole of the hind leg being brought into use. Wlien placed 

 on its back out of water it strikes out violently with both hind 

 legs simultaneously ; the hopping motion is performed in this 

 way : when walking out of the water, it moves the hind legs al- 

 ternately. 



Minutes of 

 Obs. observation. Ascents. Seconds at surface. 



No. 1 60 4 240 



„ 2 60 14 492 



Totals 120 18 732 



Summary. — The beetle rose on the average once in 6| minutes 

 for breathing, and remained on an average 40| seconds at surface 

 for each respiration. The longest interval observed between two 

 respirations was 20 minutes, and the duration of a respiration 

 varied from 1 second to 210 seconds. The time it was exposed 

 for breathing bore to the time it was concealed a ratio of 1 : ^ 9f . 

 Only two observations were made, one by night ; and it is pro- 

 bable that the species is more active by night. 



XI. COLTMBETES EXOLETUS. 



No. 1. Oct. 17th. — Observation commenced at 2.1 p.m. The 

 insect rose at 



2.20 for 40 seconds to breathe. 

 2.29 „ 65 



2.42 for 35 seconds to breathe. 

 2.49 „ 55 



At 2.51 it came out of the water and was put back at 2.56 ; it 

 rose at 2.59 to surface and stayed there 4 minutes. Observation 

 ceased at 3.4. 



" No, 2. Same afternoon 4.25 p.m. — This $ of G. exoletus rose 

 for purposes of aeration as follows : — 



4.39 for 40 seconds to breathe. 



4.51 „ 8 



5. 3 „ 20 „ 5, 



5.11 fur 30 seconds to breathe. 



5.20 „ 50 _ „ 



5.25 observation ceased. 



No. 3. From 9.7 p.m., by lamplight, the accompanying record 

 of its movements was kept. 



