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gardens near the large towns, almost every garden has its barrel filled with drain- 

 age-water. If in August we study this water, we shall find millions of mosquito 

 larvae and almost always C. pipiens larvae in them. But also in the dunghill pools, 

 where the sides of the pools are real dunghills, we often find the brown, nasty 

 fluid almost filled with mosquito larvae; they may here stand so thick that the 

 larvae almost touch each other; curiously enough the huge masses of larvae do not 

 seem to appear before August. On calm days such pools are often covered with a 

 green or reddish foam, originating from Euglena or other Flagellata. If so, it seems 

 as if all larvae in the course of a few days die off, the foam probably preventing 

 respiration, atmospherical air for larvae living under such conditions being a con- 

 ditio sine qua non. I have often found the borders of the pond covered with a 

 brown line of egg-boats. A more thorough exploration of how many times a year 

 this line appears, may probably give some information with regard to the number of 

 broods and generations. It is especially owing to the study of this line that I sup- 

 pose that the number of generations in the course of the summer is but small; the 

 examination is however rather difficult because geese and ducks have often con- 

 sumed almost the whole stock in the course of a few hours. 



But even all these localities lying near the human dwellings are by no means 

 the only spots where this species may be found. 



On examining clear, grassy ponds, which contain water the whole year round, 

 I have in August 1918 and 1919 near the border of the pond found very small 

 mosquito larvae, often in great numbers. All in all these larvae have all shown the 

 systematic characteristics of C. pipiens; still the whole exterior was different; they 

 were much smaller, of a more delicate structure, white or translucent. 



These larvae never appeared before the latter part of July, but at that time 

 they were common enough; they were pupae in the first part of August and imagi- 

 nes a little later. At the first glance these imagines did not resemble those from the 

 cisterns etc. in our dwellings; they were much smaller, and of much more delicate- 

 structure. More thoroughly studied it was however quite impossible to find charac- 

 ters which distinguished them from the real C. pipiens. In August September I 

 often found these small races in Nature, more especially over the ponds where they 

 were hatched; in our houses, on the other hand, I never saw them. In the latter 

 part of August the larvae disappeared from the ponds, and from the first days of 

 September the imagines disappeared. 



I confess that the life-history of C. pipiens is dim and obscure. More especially 

 we do not know what are the relations between the larvae and imagines in Nature 

 and those of our dwellings, farms etc. As C. pipiens hibernates in our houses and 

 the first generation is undoubtedly hatched here, I have thought that the generations 

 following were divided into some stocks which remained as house dwellers and 

 others which flew out in search of breeding places in Nature itself. Nevertheless if 

 this was the correct explanation, it is extremely difficult to understand that the 

 racial stamp could really be preserved in this way. On the other hand the total 



D K. D. Vidensk Selsk. Skr , naturvidensk. og mathem Afd. 8. Rsekke, VII, 1. 17 



