134 



in the water from the melted snow; the Aedini have only one generation. An expe- 

 dition (Knab 1908 p. 540) to western Canada was especially of great significance. 



The statements with regard to the Aedini in North America are unquestionably 

 correct; on the other hand there is no douht that some of the Aedini at all events 

 in other parts of the world are able to hibernate hoth as larva? and as 

 imagines; some of them have more than one generation in the course of the year. 

 The European literature upon this point is difficult to use mainly because the 

 determination is very uncertain. 



As mentioned above in recent years hibernating mosquito larva? have often 

 been found in Europe; most of the indications belong to A. maculipennis some to 

 the Culicines. Besides the above-named papers by Galli Valerio I refer the reader 

 to the following papers. Dupree and Morgan (1902 p. 1036), (1903 p. 88), Eysell 

 (1907 p. 210), Lacaze (1918 p. 729), Waterston (1918 p. 1), Eckstein (1918 p. 530). 

 Wright (1901 p. 882) maintains that larva? of C. pipiens and T. annulata are to be 

 found in October; exposed to severe cold they survive if the water does not freeze 

 to the bottom. Wright supposes that it is really the larva? that provide for the 

 continuation of the species through the winter in these northern countries and 

 probably throughout Europe; further, that it is during winter that the destruction 

 of the mosquitoes as larva? is to take place. This supposition of Wright's is not 

 correct. That C. pipiens can live as larva in October is really quite right, further 

 that it can endure a freezing period, but no one has hitherto found the larva? of 

 C. pipiens and T. annulata below the ice; all in all a destruction of mosquitoes 

 during the winter in the larva stage is an impossibility in our latitude. 



When finally proved, the fact that there exist mosquitoes which can hiber- 

 nate under the ice as larva?, was regarded as highly remarkable. The larva? being 

 hitherto only known as air breathing animals, we were inclined to suppose that 

 hibernation under the ice in this stage was hardly possible. In this connection 

 we shall call attention to the following considerations. 



In accordance with the fact that the larva? in winter are almost sessile ani- 

 mals their claims of nutriment are but slight, and the process of combustion there- 

 fore also very slow. Judging from the behaviour of C. morsitans in my aquaria in 

 the winter months, this supposition may be regarded as highly probable. Further 

 it must be remembered that even the iceclosed waters are only rarely quite desti- 

 tute of air-bubbles containing a greater or smaller amount of oxygen than the 

 atmospherical air. These air-bubbles derive from the green plants and are sooner 

 or later deposited under the ice. I have often seen other air-breathing insects in 

 search of these air-bubbles, and it is possible that also mosquito larva? use them 

 for respiratory purposes. 



Undoubtedly the mode of respiration of the hibernating larva? is mainly cu- 

 taneous. Exactly in the winter months the water is much better aerated than in 

 spring even in such drying ponds where all processes of decomposition on the bot- 

 tom have only a very slow course and where many green plants in drying ponds 



