SURVEY OF INVERTEBRATES 117 



a pond survived for more than 4 hours but less than 19 

 hours in water containing 2.9 cc. of oxygen per liter, 

 while Baetis rliodani from a stream died in as short a 

 time as 3 minutes in water containing 2.6 cc. of oxygen 

 per liter. The interpretation of the ecological findings, 

 however, presents difficulties similar to those outlined 

 above for the midge larvae. Fox, Wingfield and Sim- 

 monds (1937) investigated the oxygen consumption of 

 some nymphs in its dependency on the tension and found 

 that the animals could be classified as follows in the order 

 of decreasing dependency : 5«efi5 sp. - Ephemera vulgata 

 - Leptophlehia vesperiina - Baetis scamhrus - Cloeon 

 dipterum. Both Baetis sp. and Baetis scamhrus lived in 

 a swift stream while Cloeon and Ephemera were taken 

 from a pond. There exists, therefore, no connection be- 

 tween habitat and dependency of oxygen consumption on 

 tension. 



II. ADULTS 



The resistance of adult aquatic insects to asphyxia- 

 tion is not very pronounced {cf. Table 15). Plateau's 

 (1872) much quoted figures for the time during which 

 these animals can be forced to stay under water vary 

 from 3 hours in the case of Notonecta to 65 hours in that 

 of Dytiscus marginalis. But Plateau neglected to re- 

 move the air which the insects carry down with them 

 when they dive. He assumed that the oxygen present in 

 these air bubbles would last only a very short time. His 

 reasoning was faulty ; he did not realize that the oxygen 

 lost from the bubble will be replaced from the surround- 

 ing water. 



This point was first assumed to be of importance by 

 Comstock (1887) and later by Hagemann (1910) ; it was 

 then studied experimentally in a thorough manner by 

 Ege (1915) who showed that the oxygen which diffuses 

 from the water into the bubble is sufficient at winter 

 temperatures to cover the oxygen needs of diving insects 



