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teemed with enormous masses of 0. communis. Owing to the warm weather in the 

 latter part of March and in the beginning of April the development was at a some- 

 what greater speed than in the foregoing three years. Then the weather w r as bad, 

 and during the whole of April and in the first part of May .the temperature did 

 not rise above 6 -8 degrees Celsius; the w r eather was extremely rainy. Under these 

 conditions the 0. communis material was not hatched, and the pupa stage was 

 prolonged beydhd the normal limits to about two or three weeks; as the tempera- 

 ture of the water was however about six to eight degrees, all the other mosqui- 

 toes in the pond were hatched from eggs; before 0. communis left the pond as ima- 

 gines most of the larvae, belonging to the species 0. cantans, diantceus and Aedes, 

 were ready to pupate. Then when the fine summer weather arrived, all the mos- 

 quito species of the pond were almost simultaneously hatched, and in the course 

 of about a week all the species had left the pond. The pond had water the whole 

 summer but from about July to September not a single larva was found in the pond. 



Having followed the development of the species in this pond for three years 

 and having followed it in about thirty forest ponds of quite similar appearance, I 

 have seen that the above-named scheme is a true prototype of the development 

 year after year in a great number of forest water ponds ; in some of them 0. rusti- 

 cus, 0. diantceus or Aedes may be lacking, but where they are to be found, they 

 are always intercalated in the very place in the developmental series where we 

 should expect them to appear. 



Everyone who has tried to carry through an exploration of this kind, will 

 admire the almost incredible regularity with which the development of the species 

 takes place. Over an area of only a few square yards seven species have laid their 

 eggs. The eggs lie side by side in August, they are exposed to the same outer con- 

 ditions, the same burning sun, the thaw of the summed morning, the first moisture 

 from the autumn showers; one day the eggs of all the seven species can be brought 

 to swim in the very same little water-filled hole, or diminutive pond. But the seven 

 species are by no means hatched simultaneously; deep in their life history immu- 

 table laws are laid down which rule the life of each of the species. The tempera- 

 ture and degree of moisture, which forces one species to pass from one stage to 

 another, has no influence at all upon another species which only awaits its ap- 

 pointed time. 



In the temporary ponds upon the plains and meadows not overshadowed by 

 forests I have never found this highly remarkable alternation of many species. In 

 these ponds as a rule we only find two or three species: in inland ponds, mainly 

 0. excrucians, lutescens and annulipes, now and then 0. communis and rusticus; near 

 the sea shore 0. caspius, curriei and detritus. As mentioned above, also here we 

 find localities where the temporary ponds in spring all teem with larvae of one of 

 these species, and where incredible myriads are hatched in the course of a few 

 days. The rule is however that in the open country, more especially far from the 

 coast, in many localities we find a great many temporary pools in which I have 



