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new material of newly hatched larva? of the very same species which now fills 

 the pond with full grown larva?, appears. Then it is interesting to see how fast the 

 development of these newly hatched larva? goes on; especially if the weather is fine, 

 it happens that all larva?, the old ones and the newly hatched, all pupate almost 

 simultaneously; the old having taken about three weeks for their development, the 

 others, only five or six days; this is of course due to the temperatures, by which 

 the young larva? have been hatched and lived their lives, which were much higher 

 than those which regulated the rate of development of the older larvae. 



Especially the first larva stage is in spring passed in the course of a very short 

 time, commonly only a few days. If we fill an aquarium with thousands of 0. 

 communis larva', in the course of a few days we shall find the bottom of the 

 aquarium covered with thousands of small, black larva heads, provided with their 

 egg breaking tooth and thus proclaiming themselves part of the skin of the first 

 larva moult; of the rest of the skins we hardly ever see anything. Simultane- 

 ously we find in the larva swarms many larvae with very large, broad, flattened 

 and snow-white heads, which strongly contrast with the very short, dark and often 

 almost black body of the larva?. On more thorough study it proves that the head- 

 carapace is moulted much earlier than the rest of the skin, and that the new skin, 

 when leaving the old one, immediately after the moulting process, is rather dark, 

 whereas the head preserves its snow-white colour for days. 



Summary: If we combine the knowledge we have now gained of the structure 

 of the Danish mosquito larva', with our knowledge of their life, we shall in my opinion 

 come to the following result : From a biological point of view I suppose that our 

 mosquito larva? of the drying ponds may be divided into two groups: the surface- 

 and the bottom dwellers. This must not be understood to mean that these two 

 groups are quite distinct; on the contrary, they are connected with each other by 

 a long, unbroken series of intermediate stages: What I wish to point out by 

 means of the above-named statement is, that in these ponds there exist species 

 which almost always hang down from the surface, and others which generally 

 rest upon the bottom and only rarely come to the surface. Both groups use 

 the atmospherical air for respiratory purposes, but to the latter group the 

 respiration through the skin is of much greater significance than to the former; 

 further the nutriment of the first-named group takes place when the larva 

 is suspended from the surface, that of the last-named mainly from the bottom; 

 the first-named group are plancton- and suspended detritus feeders; the last- 

 named scrapes microscopical organisms and deposited detritus from the decay- 

 ing leaves, or twigs, or seeks its nourishment in the diatom-coverings etc. upon 

 living plants. 



It is of course self-evident that animals which live their life in these two 

 entirely different ways, cannot be constructed in the same way. 



Larva? which always hang down from the surface, taking in atmospherical 

 air, need not resort to respiration through the skin. If we combine my own 



