58 



cin larvae which, when hatched, always give 0. excrucians. In one of the ponds the 

 larvae appeared 16/iv 1918 (Hestehave Hiller0d), a few days after the ice had dis- 

 appeared; they were full grown 30/iv and pupse Wv. At that time there was only 

 a few centim. of water in the pond; though the temperature of the air was only 

 eight degrees C., the temperature of the water was twenty. In 1919 the develop- 

 ment was quite the same as in 1918; pond icecovered 25/iv; full grown larvae 2/y; pupae 

 i/v. The pond was dried up by i/vi. In 1920 the ponds were already icefree in 

 the latter part of February, but the 0. excrucians larvae did not appear before the 



Textfig. 4. Pond: Hestehave, Hillerad. O. prodotes, O. excrucians, O. cantans. 



middle of March; they were fullgrown in the first days of April; bad weather was a 

 hindrance to further development; pupae did not arrive until 8/v; imagines not 

 before Wv. In May 1920 I found the O. excrucians larvae in the ponds of the Ere- 

 mitage plain. Now and then I have also found the larvae in the common forest 

 ponds teeming w r ith 0. communis larvae. It was on 2l/y in such a pond, in Arne- 

 have forest near Tjustrup, that I observed this fact. On a day with bright sunshine, 

 standing near a pond with huge swarms of 0. communis-\ar\se hanging down from 

 the surface, I saw that below the layer of the perpendicularly hanging 0. co/n/nums-larvae 

 there was another layer of almost horizontally standing Culicin-larvae; they were 

 larger and almost white; most of them rested on the bottom or got support from 

 the fine leaves of Hottonia. These larvae were caught, isolated, and eight days later 

 gave O. excrucians. 



