knew well which would give the best results, if more thoroughly studied. In accor- 

 dance with this knowledge twenty-five temporary forest ponds were selected, and 

 in the time 1916 — 1919 subjected to a regular fortnightly exploration. After the 

 establishment of the Freshwater Biological Laboratory at Tjustrup lake, near Soro, in 

 the middle of Seeland, I soon found 15 other ponds, mainly belonging to the open 

 meadows and large plains which were simultaneously included in the exploration. 

 The ponds were explored every fortnight, viz. during the winter, when the ponds 

 were frozen and covered with snow, at longer intervals, but in spring, when the 

 different larva? appeared, and the imagines arrived, as often as possible, i. e. many 

 of them almost every day. The ponds were so selected that in the course of a 

 single excursion I could reach from five to seven. On schemata the results of every 

 excursion were noted and observations with regard to the freezing and drying 

 periods taken down. At first I took the temperature of the ponds, but later on I 

 learned that this was quite useless; on sunny days the temperature might be 

 about thirty degrees Celsius, the next day, if the weather was cold and rainy, only 

 about ten. The temperatures could only acquire, scientific significance if I had 

 been able to indicate the total sum of heat-units which in the course of the year 

 was conveyed to the ponds. As this was impossible, the temperatures were not 

 regularly taken. 



In 1916 I thought that I should only find very few mosquitoes in the diffe- 

 rent ponds; in Denmark we had hitherto, viz: St.eger in his valuable old work: 

 Systematisk Fortegnelse over de i Danmark hidtil fundne Diptera, only found ten 

 species of Culicini and of these two were doubtful (C. annulipes Meig. and C. nigripes 

 Zett.) and one restricted to brackish water; the greatest number that I could ex- 

 pect to find, in my area of distribution, was therefore only seven. At that time I 

 had not the slightest idea that the determination would cause troublesome diffi- 

 culties. I supposed that I could only expect to clear up the biology of the well 

 known species: C. nemorosus Meig., cantans Meig., orncttus Meig., pipiens Linne and 

 annulatus Schrank; further I did not know that the larvae of these species practi- 

 cally speaking were quite unknown, or at all events insufficiently described; the 

 valuable work of Meinert: De eucephale Myggelarver 1886, deals only slightly 

 with the larva 1 of Culicini. Already in 1916 I understood that this number would 

 be augmented with several new species, but the determination of these species was 

 quite impossible to me. A closer examination of the large larva material from the 

 many ponds, worked out in the winter months, showed that there were especially 

 some ponds, which must be examined with special care next year. In 1917 these 

 ponds were examined almost weekly from lf> April to the first part of July. In this 

 time I then saw from five to seven species appear and disappear after each other. 

 Some of them were detected in the larva stage, separated in this stage, and then 

 hatched in special vessels; others appeared from larva material which I lirst 

 thought was homogeneous. In 1917 I had demonstrated about 1,") different species, 

 and in 1918 I tried to elucidate the biology of all these species. To my great satis- 



