Anatomical description 
of the larva of Mansonia Richardii (Ficalbi) 
found in Danish freshwaters. 
By 
C. Wesenberg-Lund. 
Introduction. 
On an excursion in September 1914 to one of the little ponds 
near Donse in the north-eastern part of Seeland, a locality well 
known to botanists and zoologists, I was sitting in my boat near 
2 sunlit, prominent point of the shore. Some plants were laid upon 
a tray half filled with water. While searching for larvæ of Coleo- 
Ptéera my attention was now and again attracted by some large 
Mosquito larvæ which crept over the bottom in a serpentlike man- 
her, when the tray was shaken. It struck me, that it was really a 
Peculiar season to find full-grown Culex-larvæ. I caught one of 
them and placed it into a high cylinder-jar. To my astonishment 
I saw, that the animal undoubtedly was heavier than the water 
and that it sank slowly downwards and settled itself horizontally 
on the bottom. Moreover I saw, that the animal did not at all 
Swim like a common Culex-larva, but it always swam horizontally; 
it was extremely sluggish and had a milky-white colour, very dif- 
ferent from the brown colour characteristic for all our Danish 
Culex-larvæ, 1 could observe that the sipho- was of a peculiar 
Structure, but on using a lens with high power I immediately 
understood, that I had made one of the most remarkable discover- 
ies we have made here in our freshwaters for a long time past. 
Some weeks before, I had received a separate copy from Dyar 
and Knab (Entom. News 1910 p. 259) relating to a peculiar mos- 
quito-larva, Mansonia perturbans; the paper was cited in my 
Work on the Water Insects (1915), then just in press. The larva 
