16 



lobe, the palatum, and two large lateral lobes, flabella?; the whole preantennal 

 region of the head and the relations between the labial folds and the black-pigmented 

 apodemes which enter the flabellse and to which the muscles are fastened are well 

 described by Thompson (1905 p. 145). Here we shall restrict ourselves to some 

 remarks with regard to the different development of the hair-coating in the diffe- 

 rent species. 



As far as I can see, we find two quite different types of hair-structures on the 

 labium. In one group the hairs of the flabellse are all of almost the same kind; 

 long, soft, yellow hairs. Only the length of tbese hairs is very different in the different 

 parts of the flabellse. Sidewards and nearest to the outer margin of the flabellse 

 they are very long; inwardly and nearest to the palatum they are shorter and 

 have another direction; those of the outer margin are held vertically on the 

 longitudinal axis of the head, those of the inner margin are parallel with it. The 

 large brushes are therefore divided into two parts, a horizontal and a vertical 

 brush, which are separated from each other by a curve; this is most conspicuous 

 in C. morsitans, C. pipiens and nigritalus, Tceniorhynchus Richardi, but it is also to 

 be observed in 0. diantceus and Aedes cinereus. When these species, especially C. 

 morsitans, are observed with the binocular}' aquarium microscope, we see the large 

 horizontal rami of the flabellse regularly thrust out and in, being expanded and 

 folded together; in the part held horizontally the hairs are pressed together and act 

 against the water as a compact mass; in the part held vertically (the inner part) the 

 hairs are spread out from each other during the stroke outwards, but undulating 

 motions from without inwards may be observed during the strokes. By means of 

 these undulating motions particles caught by the outer rami are carried downwards 

 to the mandibles and then seized by them. We find this type of hair development 

 on the labium in all those species which, when undisturbed, always hang down 

 from the surface and seek their food in the water layers. This food only consists 

 of all the small particles floating in the water which, by means of the large lateral 

 hairtufts, are carried with the water-currents down to the mouth. 



In all other Danish mosquito larva? we find quite another type of hairs and 

 hairbrushes; the hairs are almost all equally long, there are no large, horizontally 

 extended flabellse; seen from above the whole apparatus conveys the impression of 

 a compact brush with most hairs arranged in a circular row, inserted nearest to 

 the edges of the brush. Further there is the great difference that the hairs nearest 

 to the palatum have quite another form; they are elegantly curved, flattened, and 

 bear upon their inner side from ten to twenty short teeth; the hairs are changed 

 into combs, and the whole apparatus is a combing apparatus, mainly used in 

 a way quite different to the corresponding one by the above-named species. Most of 

 these larvse hang down from the surface, producing water currents by the expand- 

 ing and unfolding of the hairbrushes. Still they are also able to get their food in 

 quite another way. Living in ponds, often with extremely small volumina of water, 

 they go down to the bottom, where they brush and comb off the sedimented par- 



