faction I saw that I almost always might be sure that the different species year 

 after year were hatched in the same ponds and almost always at the same tempera- 

 ture. As the larva? appeared in the ponds, they were separated, and about a hun- 

 dred placed in a special vessel and the vessel set in a hatching cage. The skins 

 were preserved and where I got a quite homogeneous imago material from a vessel, 

 I was sure that I had the right connection between larva and imago. 



In 1919 many doubtful questions were tried and tried again; and several of 

 them were now nearer to being solved; especially the group 0. nemorosus, was ex- 

 tremely troublesome. Again and again I came to the conclusion that there are species 

 which may easily be distinguished in the imago stage, but which as larvae cannot 

 be distinguished from each other; further that there are species which as larva? 

 may be distinguished at a first glance, but as imagines are almost indistinguishable. 

 At this time the final determination of the species was desirable; most of them at 

 that time had only numbers. Having myself tried to determine the material, I saw, 

 that if I used the ordinary works on the European mosquitoes for some of the 

 most characteristic species, this gave no result. I then reguested my friend Prof. 

 Simon Bengtson of Lund to compare some of my material with Zetterstedt's speci- 

 mens in Lund; as I however compared the determinations with my larva material 

 I saw that somewhere there must be some mistake. I then sent some of the most 

 troublesome species to Mr. Edwards at the British Museum and asked him to look 

 them over. From him I got the wholly unexpected result that, in my material, 

 there were no less than three American species: 0. abfichii (Felt), fletcheri (Coquil- 

 let) and diantceus (H. D. K.), which have hitherto not been found in Europe; in a 

 following collection Mr. Edwards then determined a fourth species 0. prodotes 

 (Dyar), which also hitherto was only found in America; this species I had over- 

 looked; having examined the preserved larva material from the pond in which 

 this species should have been hatched, I really found a very few highly charac- 

 teristic larva? which most probably belonged to this species. Next year these larva? 

 were found again in the same pond, separated and, when hatched, really gave 0. 

 prodotes. Later on it was found out by Mr. Edwards that 0. fletcheri was identic 

 with 0. lutescens (F.) and 0. abfichii with 0. excrucians Wlk. Mr. Edwards 

 further came to the same conclusion as I, that the old species C. ornatus Meig. could 

 not be found in my material; those determined by St.eger and now in the collection 

 of the Boyal Museum, Copenhagen, being partly Culicella morsitans, partly C. com- 

 munis. As these species, apart from 0. prodotes, which was studied in 1920, were 

 separated as numbers already in 1918 and with regard to all biological data proto- 

 colled separately, it will be understood that with regard to the biology of the species, 

 it was not of the slightest significance that they were not finally determined till 1919. 



In 1920 two questions had to be solved before the work could be finished. 

 As the two freshwater laboratories in Hillerod and at Tjustrup were both situated 

 far from the sea-shore, I had no opportunity to study the sea-shore mosquito 

 fauna, where the habitat of 0. dorsalis Meig., already found by Staeger, really is. 



