8URVEY OF INVERTEBRATES 109 



and Mudrezowa-Wyss (1930) can be disregarded, since 

 the early death of the animals in their experiments may 

 have been due to a toxic influence of hydrogen sulfide 

 rather than to a lack of oxygen. The metabolism of the 

 larvae has unfortunately never been studied at low oxy- 

 gen tensions. It is therefore at the present time im- 

 possible to decide whether or not the anaerobic functions 

 which they unquestionably possess play a significant role 

 in their natural surroundings. 



It has been pointed out (Varley, 1937; Krogh, 1941) 

 that a number of other aquatic insect larvae — those of 

 the syrphid fly Chrysogaster MrteUa, of the rice water 

 weevil Lissorhaptus, and of the mosquitoes of the genera 

 Taeniorhynchus, Ficalhia and Mansonia — normally ob- 

 tain their oxygen in the same way as the Donacia larvae. 

 It would be of great interest to study experimentally 

 their reactions to low oxygen tensions or to complete 

 lack of oxygen. Krogli (1941) alone has performed some 

 experiments on the Mansonia larvae. He states that their 

 viability was not impaired in an atmosphere containing 

 only 3.4 per cent oxygen but that they became paralyzed 

 in pure nitrogen. 



The mosquito larvae that normally obtain their oxygen 

 directly from the atmosphere by means of their breathing 

 trumpets, like the Culex or Anopheles larvae, seem un- 

 able to lead an anaerobic life for long periods of time. 

 One of the best known means of combating malaria is 

 the asphyxiation of the vectors by covering the water 

 surface with a layer of oil. This prevents the larvae from 

 getting oxygen from the air but obviously does not pre- 

 vent them from utilizing the oxygen dissolved in the 

 water. Thus Fraenkel and Herford (1938) found that 

 Culex larvae submerged in oxygenated water, were still 

 able to consume about half as much oxygen as they 

 normally use when they have access to the surface. It 

 would seem that not even a jDartial transition to anaerobic 

 processes is possible, at least not for long periods. Ba- 



