62 



other very much: in the meadows near the outflow of Susaa in Tjustruplake, on 

 the large moors south of Arres0 and on the southern coasts of the island Lolland. 

 The large meadows near the outflow of Susaa in Tjustruplake only a kilom. from 

 my summer laboratory are regularly inundated in the winter; ice covers the whole 

 area and in spring it is changed into a large lake. In May the water disappears, 

 and herds of horses and cattle graze in the vast meadows, dry from June to No- 

 vember. Some of the pools left were under direct observation for almost three years. 

 In the spring of 1917 the ponds contained plenty of larvae which were full- 

 grown in the first part of June; the larvae were hatched in my laboratory and gave 

 0. fletcheri. In Nature they w r ere hatched about Wvi, on i/vn the pond was dry, 



Textfig. 5. Pond near Tjustrup-lake. O. lutescens, rusticus. stamm phot. 



and the bottom was covered with grass which w r as cropped by the cattle. The 

 pond was never filled with water before the middle of November, and by iVn 1918 the 

 pond contained many mosquito larvae, but only O. communis; from the middle of 

 January and till the latter part of March the pond was ice-covered, and when the 

 ice had disappeared crowds of mostly fullgrown 0. communis larva? appeared. On 

 12/iv I found a great number of newly-hatched yellow larvae; they did not swim 

 as the O. communis larvae and only rarely hung down from the surface, but moved 

 in smaller or larger circles along the sides of the aquarium; the larvae in my cul- 

 tures were fullgrown by 23/iv and metamorphosed into pupae on 30/ IV . On 4/v the 

 imagines appeared. In Nature the whole stock of larvae died off. On so/iv the 

 temperature fell below zero and heavy snow fell at 9 o. cl. a. m.; the low tempera- 

 ture retarded the development and, as the pond was wholly dry about 15/v, the 

 whole mass of larvae died off. - - Other ponds near this, which were somewhat 

 deeper, were filled with water till July, and in these ponds the development was 



