45 



wholly dry ; the pools are however often filled with brackish water which is stagnant 

 for months in winter and spring, but soon evaporates in summer. In rainy sum- 

 mers the pools hold the water for a shorter or longer time. 



In autumn again most of the pools are often red from pur-pie sulphuric bacteria 

 and are bordered by Scirpus maritimus, Aster tripolium a. o. plants. At certain periods 

 they contain thick layers of green algse, and it is only in those pools, the bottom 

 of which are covered with a layer of algse in decomposition, that we find the huge 

 masses of larvae. The above-named dike forms a very distinct border-line between 

 the mosquito fauna of the area; landw r ards in the numerous drying ponds enorm- 

 ous swarms of 0. communis are hatched. The first larvae were found on 24/ni; they 

 pupated and were hatched as imagines in the time from 21/jy to Vv. The whole 

 area was inundated and almost impossible to cross. As the water fell again clouds 

 of 0. lutescens appeared, and a very few belated larvae were found on 9/vi. j n fae 

 last part of May and in the first part of June 0. lutescens has most probably popu- 

 lated the numerous ditches. As 0. rusticus was found in the last part of May as a 

 regular tormentor on stretches bordering the meadows, it is probable that some of 

 the holes have been hatching localities for this species. 



Outside the dike between it and the sea no larvae of mosquitoes were found 

 during the whole of April and first part of May; in the brackish water pools Nereis 

 diuersicolor, Crangon vulgaris, and other marine animals were common, but always 

 in company with Corixce, various Hydrophilidce and Dytiscidce. On 26/v mosquito 

 larvae were for the first time pointed out in these ditches; in the samples were 

 enormous amounts of newly-hatched larvae, some halfgrown larvae but no full 

 grown ones; most probably the hatching process was not more than a week old. 

 Already by 12/vi many of the pools were dried up, and by 16/vi all pools were wholly 

 dry. In the time from 26/v to about 15 /vi, i. e. about three weeks, enormous masses of 

 0. caspius were hatched; in the material also appeared the supposed 0. curriei, but 

 I was never able to find any differences in the larva material, though many thou- 

 sands of larvae have passed under the binoculary microscope; once only I also 

 found a larva of 0. lutescens, and on the coast of Sealand nearer to human dwellings 

 larvae of C. pipiens and of a few T. annulala often appeared. In the two first weeks 

 of June numerous 0. caspius were sitting in the grass round the holes; in the last 

 part of June they left the locality and began their attack nearer the town where 

 we in the evening, were attacked by them, 0. lutescens and rusticus. 



In the time from 16/vi to 8/vii all pools were quite dry; then when Mr. KRY- 

 GER returned to the locality on 2/vm the pools were full again after the rainy 

 summer; they now contained incredible numbers of larvae, the water was black; again 

 the holes were visited, and in the last part of August the whole stock was hatched. 

 Again enormous masses of 0. caspius were hatched; in the last part of August they 

 were found nearer the human dwellings, and in the whole of September they tor- 

 mented the inhabitants of Copenhagen. In order to clear up the manner of hiberna- 

 tion I explored and got information from many buildings in the outer part of the 



