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rather peculiar form and the swimming-brush more reduced than in any other of 

 our Danish mosquito larva?; of the anal gills two are extremely large and broad, 

 and the hair-covering of the body, more especially that of the abdomen, unusually 

 highly developed; further, the colour of the larva is greyish-white and the whole 

 larva semitransparent. Finally the tracheae are remarkably broad, flattened. Many 

 of these peculiarities may also be pointed out in many of the tropical mosquito 

 larvae living under similar conditions; this more especially holds good for the equip- 

 ment of hair-bristles, which are often more luxurious in tropical species, further 

 with regard to the small eyes, the slight development of the anal brushes, of which 

 the ventral one may be wholly absent, and the large broad trachea gills. There is 

 an easily comprehensible connection between the small eyes, the slight development 

 of the swimming-fan and the conditions under which the larva? live; on the other 

 hand the luxurious development of bristles, and more especially that of the large 

 anal gills, is difficult to understand. It must be taken for granted that respiratory 

 conditions on the bottom of these holes are extremely bad; it is therefore difficult 

 to comprehend how the cutaneous respiration, taking place either through the cutis 

 of the abdomen or through that of the anal gills, can help the larva to any con- 

 siderable extent. 



Having found the larva; in the forest of Suserup, where the summer labora- 

 tory is, later on I found the larva in the neighbourhood of Hillerod, by Dragsholm, 

 by Tidsvilde (North Sealand near the coast of Kattegat). The imagines have never 

 been found in Nature itself; all the specimens in my collection derive from my 

 aquaria; the imago is of course extremely rare and probably very difficult to detect. 

 In such a little wood as that of Suserup every single tree has been observed; the 

 wood does not possess more than twenty breeding localities; if there are only hatch- 

 ed about thirty-forty mosquitoes in every hole, it is intelligible that the imago 

 must be rare and almost impossible to detect. I have further observed that spiders 

 almost always weave their webs over the holes; the webs standing only a few cen- 

 timeters from the surface, almost every flying animal leaving the surface must be 

 caught by the webs. 



Having had the holes under regular observation for about two years, I feel 

 quite sure that we have only one or two generations the whole year round. In 

 1918 many of the holes were ice-covered during the last days of March; they were 

 filled with water during the first days of April and in the time from April the first 

 to about April the fifteenth very many larvae in the first stage were found in the 

 holes. In the first weeks of May many of the holes were almost dried up; the larva' 

 only grew very slowly, lying between the moist leaves at the bottom of the holes, 

 but without any water to swim in. In the latter part of June the holes got some 

 water and the larvae grew more quickly, but no pupa- were observed before the 

 first days of July; in the course of July all the pupae were hatched, owing to the 

 extremely rainy summer- the holes almost always held water. From the last days 

 of July no larvae could be observed in the holes. In 1919 and 1920 I found a few 



