110 SURVEY OF INVERTEBRATES 



bak (1912) also observed that Culex larvae become as- 

 phyctic in a few hours when completely immersed in 

 water, but if truly anaerobic conditions are established, 

 they are asphyxiated already in 95 minutes. The larvae 

 of Theohaldia annulata, submerged in water apparently 

 saturated with oxygen, usually die on the fourth day, 

 although a few are still alive on the fifth day (Sautet, 

 1936). It would be of interest to study the Aedes larvae 

 at low oxygen concentrations, since Gjullin, Hegarty and 

 Bollen (1941) found that a low oxygen concentration 

 (about 3 mg. per liter) greatly favors their hatching 

 from the eggs, while this is not the case with Culex, Ano- 

 pheles or Theohaldia. 



The fact that living mosquito larvae are occasionally 

 found in water covered by ice, i.e., severed from direct con- 

 nection with the atmosphere, does not contradict the above 

 view. Not only will their metabolism be low at these tem- 

 peratures, but gas bubbles will also frequently be found 

 below the ice covering and from these the larvae can get 

 oxygen in the normal manner. It is obvious that as the 

 oxygen is withdrawn from the bubbles by the larvae, it 

 will be replenished from the surrounding water, since 

 a gradient will be established as a result of the oxygen 

 consumption. 



Much more resistant to lack of oxygen than the forms 

 hitherto named are some larvae that occur rather regu- 

 larly in the deep zone of lakes, especially the cJiirono- 

 mids and Chaohorus {Coreihra) larvae. 



The fact that the chironomids are not exacting with 

 respect to the amounts of oxygen present in their sur- 

 roundings seems to have been emphasized first by Miall 

 (1891). Since his time many observations have come to 

 light indicating that a number of species survive rela- 

 tively well both the summer- and winter stagnation pe- 

 riods in eutrophic lakes (Juday, 1908; Muttkowski, 1918; 

 Thienemann, 1918; Eggleton, 1931 ; Lindeman, 1942). Not 



