iii the snow-water of early spring. Southward the appearance of the larvae is govern- 

 ed by the formation of pools by heavy rains and consequently occurs at irregular 

 intervals. It has especially been studied by KNAB at Saskatchevan with other mos- 

 quitoes of the large prairies (1908 p. 540). 



Biology. For a long time it has been a well-known fact that countless mos- 

 quito-masses are a real plague to all the suburbs of Copenhagen, especially those 

 lying near Kalvebodstrand, the strait between Copenhagen and Amager; one of these 

 suburbs, Valby, has given the mosquitoes of this district their name, they have 

 been called the Valby mosquitoes; they appear almost every year, more especi- 

 ally at the beginning of August; later on they spread over Copenhagen, being most 

 common in the large park Frederiksberg-garden, the Royal Garden, at Lange Linie 

 and northwards along the shores of the Sound. These mosquitoes belong almost 

 entirely to one and the same species 0. caspius. Curiously enough they have hitherto 

 only been found in the vicinity of Copenhagen, and it has hitherto not even among 

 zoologists been a well-known fact that Copenhagen had its own special mosquito, 

 hitherto only found in it and in its neighbourhood; indeed we also find C- pipiens 

 and T. annulata, but these two species do not, as far as I know, attack people, at 

 all events not like the above-named species; a few specimens of 0. communis, 

 lutescens and canlans may be found in the parks, but they are of no great conse- 

 quence. - - It was of course most natural to search for the hatching areas of 0. caspius 

 in the old locality of Amager where STAGER had found them almost a century ago. 

 As I wished to make a special study of our brackish-water mosquitoes and my 

 time was too much occupied with other mosquito-work, I asked Mr. KRYGER in 

 1920 to explore the brackish water coast of Amager and Seeland from Copenhagen 

 and southwards towards the bay of Kj0ge at regular intervals in the time from 

 medio Marsh to September. In the time from 24/m to 8/vn he made twenty ex- 

 cursions at regular intervals; then he was on a journey in Jutland from 8/ V n to 

 l/vin and in the time from 2/ V m to 2 <Vix five excursions were undertaken. From 

 every excursion he brought living material to my laboratory, and thousands of 

 specimens were hatched in the hatching cages. 



Most of the explored area belongs to the Amager common lying between Kalve- 

 bodstrand and the little village of Taarnby; it is used by the soldiers for gunpractice, 

 and is now therefore rather difficult to use for study of nature. The whole country 

 is extremely flat, the height over the sea leavel being only a few feet; formerly the 

 sea often covered the whole area and after heavy showers, especially in spring, it is 

 even nowadays changed into an almost inundated area which is difficult to cross. 

 From the plain it is now separated by a dike along which a channel runs land- 

 wards. Between the dike and the sea numerous brackish water pools are to be 

 found; on the other side, scattered over the flat ground, countless small holes may be 

 seen. After June the whole plain is commonly quite dry, and cattle and horses are 

 driven over the rich meadows. The area between the dike which prevents the sea 

 from inundating the plain, is filled with brackish water pools; after June commonly 



