58 



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

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

 appeared; they were full grown 30/iv and pupa? 14/y. 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 larva? 2 /v; pupa? 

 10/v. The pond was dried up by 1/vi. In 1920 the ponds were already icefree in 

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



Texttig. 4. Pond: Hestehave, Hillerad. 0. prodotes, 0. excrucians, O. cantans. 



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

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

 before 15/v. In May 1920 I found the 0. excrucians larva? in the ponds of the Erc- 

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

 ponds teeming with 0. communis larva. It was on 2i/v 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. communisAarxvc hanging down from 

 the surface, I saw that below the layer of the perpendicularly hanging 0. communis-larvae 

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

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

 the line leaves of Hottonia. These larva were caught, isolated, and eight days later 

 gave 0. excrucians. 



