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observations with regard to the biology and anatomy of our own little mosquito 

 fauna with the remarks with regard to biology and the drawings in the large 

 work of Howard, Dyar and Knab, we shall come to the general result that we 

 find the slightest development of the tracheal gills in the surface feeders, and the 

 strongest development of these organs in the bottom feeders. Only where we have 

 to do with larva? which are really surface feeders, but hibernate below the ice and 

 therefore for a great part of their life are shut out from the surface, do we find highly 

 developed tracheal gills. Larva' from brackish water Ochlerotatus caspius, 0. detritus 

 seem regularly to have very short, button-shaped tracheal gills. 



As plancton-eaters the surface-dwellers must possess large, fanshaped organs, 

 by means of which water currents, which carry the organisms and detritus into 

 the mouth, are produced; this extremely fine material must further be caught by 

 organs which are so constructed that the same water currents do not release it 

 again. On the other hand the material is triturated to such a degree that a further 

 subdivision is almost unnecessary; we therefore find that in the surface dwellers 

 {Culiceta morsitans, Cnlex pipiens, nigritulus) the fiabellse of the labrum, the fringe of 

 the mandibular, and the apical hair-tufts of the maxillae are all highly developed, 

 whereas the triturating part of the mandibles is always feebly developed. 



On the other hand, in the bottom feeders, the material destined for nutriment 

 is not suspended in the water layers, but of a much coarser solid condition, and 

 must be scraped off from solid bodies and not, like suspended material, be whirled 

 into the mouth; in accordance with that we find feebly developed flabelkv, with 

 many of the hairs transformed into comb-bristles which we only rarely find 

 developed in the surface dwellers; the fringes of the mandibular are more slightly 

 developed, and the hair-tufts on the maxilla? may be wholly absent (T*. annulatd). 

 On the other hand the inner edges of the mandibles are provided with strong 

 thorns which may be dentated, and the triturating part of the mandibles is very strong. 



With regard to the main organ of locomotion, the great swimming brushes, 

 it would seem upon more superficial consideration, that this organ has not been 

 influenced by the different mode of life in the two groups; still it must be pointed out 

 that some of those larva? which are very sluggish and live in extremely small water 

 masses, such as F. geniculata or the great group Sabethini, have either very few hairs 

 in the tufts of the swimming fan (F. geniculata only two) or totally lack the ventral 

 fan (Sabethini). In many of the bottom feeders, f. i. T. annulata, we find a highly 

 developed fan with a large number of hairs in the tuft (about fifteen). 



Finally it may be pointed out that in the Danish fauna we always find the larva- 

 with the longest siphones among the surface dwellers, and those with the shortest 

 among the bottom dwellers; further that pecten and comb in the surface dwellers 

 differ very much from those of the bottom dwellers; as we are however quite un- 

 able to understand these structures, we cannot further comment on. though we are 

 forced to pay attention to, these facts. 



On the other hand it must be taken for granted that there is a connection 



4* 



