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before June, often not till the latter part of June. The eggs are laid singly and 

 often in the same pools in which the imagines are hatched, but these pools are now 

 dry, and the eggs are deposited upon dry bottom from July — August to December — 

 January and do not hatch before a freezing period; the males probably die off 

 shortly after the mating process; the number of males I have seen after June being 

 very limited. In some ponds, and more especially in rainy summers, larvae may be 

 found after June, but the number is always very limited and has no great signifi- 

 cance, neither for the species nor for man. 



0. communis has as a rule not more than one generation. In the very rainy 

 summer of 1919 many of the ponds were never dried up, and a good many had 

 plenty of water almost the whole of the summer. Of course we should now expect 

 that a new generation would be hatched, but this, as far as I can see, is not the 

 case. - - In these ponds I have really found 0. communzs-larvae in the months of 

 July — August; but the number was always small, and I never found those vast 

 swarms of larvae and pupae which coloured the ponds black in spring. The 21st of 

 July was the last day I found 0. nemorosus larvae; to these lately hatched 0. commu- 

 nis larvae, I refer most of those imagines which torment us in August and Septem- 

 ber. Even on 12/ix a single 0. communis stung me in the Royal Park at Hillerod. 

 In autumn when the small ponds are filled again, as a rule we find no O. commu- 

 /n's-larvae; here and there I have seen a few, and once I got a pupa which meta- 

 morphosed into imago H/xn in one of the aquaria. 



I am inclined to regard all these larva' which appear after the great hatching 

 period in spring, not as belonging to a new, second generation, but to the same 

 generation as those which were hatched in spring. I suppose they derive from eggs, 

 which have had a rather unfortunate situation, which the water has reached too 

 late, or which have been buried too deep under the remains of the decaying vege- 

 tation. I do not think that we have to do with a new generation, hatched from 

 eggs laid in summer, whilst only very few larva; are hatched, and whilst the same 

 ponds in which these larvae are hatched, teem with larvae the next year. 



It may be added that more than once I have observed ponds which had 

 water till June in 1917 and which were hatching-places for swarms of mosquitoes 

 about 7/v; in 1918 the very same ponds did not get any water and were dry the 

 whole year. In 1919 in April the ponds got water again and now teemed with 

 larvae in May; I suppose that these larva? belong to eggs which have preserved 

 their vitality from 1917. 



That 0. communis really can have two generations in a year, we shall see 

 from the following fact. 



On an excursion 25/ x 1918 through the forest Store Dyrehave near Hillerod I 

 found many small ponds filled with water; heavy showers during the last fortnight 

 had given so much water that the bottom in the hollows could not take up more. 

 To my great astonishment in two of them I found enormous masses of black, al- 

 most fullgrown mosquito larvae. The ponds were overshadowed by high spruce firs, 



