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the principal reason, why the imago is comparatively rare in our country and much 

 rarer than the larva. But the peculiar circumstance that we hardly ever find the 

 larvae in the swarms of 0. communis, though they are by no means rare in the 

 ponds, is caused by the fact that the larvae of C. morsitans conceal themselves 

 between the decaying leaves and only rarely come to the surface. This is in ac- 

 cordance with observations made by Eckstein (1918 p. 533), and Lang (1920 p. 102). 

 In my aquaria the imagines from larvae taken into the laboratory in December, 

 appeared already in the two first weeks of April ; I therefore thought that this 

 would also be the case in Nature. It therefore astonished me extremely to find that 

 in the last days of the hatching period of 0. communis black and much larger 

 pupie appeared from which later on C. morsitans were hatched. A more thorough 

 study of my temperature observations this year and new observations next year 

 showed, firstly, that these ponds were all filled with water during the winter 

 and further, that the larva of C. morsitans in spring as in winter hardly ever 

 came to the surface, but lived near the bottom or were hanging down from the 

 plants. If this is a general rule, the life as larva of this species may be remark- 

 ably long, lasting from the last fortnight of September to the last half of May; in 

 the five last months, as far as I know, that larva does not moult. That the pupa; 

 in May really derive from hibernating larvae and not from a new spring generation 

 I regard as certain, the pond in April — May being under regular observation almost 

 every week. 



I therefore feel sure that C. morsitans in our latitudes has only one generation; 

 laid as eggs in the summer months, living as larvae from September to May, as 

 pupae only a few days, and then from June to autumn as imagines, the latter dying 

 out before autumn. 



As imago the mosquito, as stated above, is rather rare; this is the case at all 

 events in North Seeland. I have taken it from June to the middle of August, but 

 always only in small quantities; in July the mosquitoes where filled with eggs. I 

 suppose that the egg-laying process took place in July — August; the eggs were laid 

 upon wholly dry soil, the ponds where the larvae appear in September all being 

 dried up during the summer months. As a female in a vessel without water, but 

 with the bottom covered by dried leaves, had laid her eggs singly or in small 

 batches, I take it for granted that the females also in Nature throw their eggs 

 singly or perhaps in small lots between dried leaves and withered grasses on the 

 spots where they were hatched in spring, and which will again get water in autumn. 



As the mosquito lives as larva at very different temperatures, from about 

 15 — 20° C. in May and September and near zero in winter, we have an excellent 

 opportunity to study the different manner of life at different temperatures. As regards 

 respiration there is a great difference between the behaviour of the larva in autumn 

 and winter and in spring. Like most of our other mosquitoes C. morsitans is sup- 

 ported by the surface film in the autumn and like other Culicin-larv;v breathes 

 atmospherical air. When winter comes as the temperatures falls, the larvae dis- 



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