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now be understood, that the motion up and down of the anal seg- 
ment, when the larva is sitting with the tip of the sipho pressed 
against the plant, will be transferred through the muscular system 
to the chitin rod, and from this to the inner tube. By the strokes 
of the tail the tip of the sipho is forced into the plant-tissue. 
If we regard the sagittal section of a Culex sipho (fig. 34) 
we will find the same small muscle (y) connecting the muscular 
system of the sipho with that of the tail (th segment). We will 
understand, therefore, that also in the caese of the Culex a trans- 
mission of power takes place; but here it has quite another im- 
portance. When the Culex-larva, super-compensated, with the sipho 
upward directed, arises towards the surface, the closing-apparatus 
is closed; when the animal arrives to the surface, the bristles on 
the flaps break the surface-film, and by contraction of the muscles 
the flaps are separated and spread out upon the surface; then there 
is free passage for the atmospherical air to the tracheæ; the larva 
hangs down from the surface supported by the surface-film. During 
the ascent the tail is not used at all. 
The process is quite different when the sipho is going to be 
relaxed from the surface. Then we see very often, and espec- 
ially when the larva is frightened, the animal making some very 
vigorous strokes with the tail. These strokes just relax the clo- 
Sing-apparatus from the surface. Altogether the swimming-brush 
in the Culex has quite the same function as in the Mansonia. 
The only difference is to be found in the medium from which the 
air has to be taken. Mansonia is obliged to pierce the sipho into 
plant-tissues; the common mosquito larva must push it through 
the surface-film; the swimming-brush of the Mansonia tail is the 
main organ enabling the animal to force its way into the air; in 
the case of the other mosquito larvæ the organ is, in this regard, 
often unnescesary, and the only importance of the tail is that of a 
Swimming-organ. But whatever the Culex-larva shall leave the sur- 
face or the Mansonia its twig, we see in both cases the larva get- 
ting free from the supporting medium by means of the tail. 
Finally it must be added, that the earlier decriptions of the 
Ssipho of Mansonia have been rather incomplete. As stated by 
.D. K., the shape of the sipho is rather different in the two 
Mansonia larvæ hitherto described. With regard to M. perlurbans 
Vidensk. Medd. fra Dansk. naturh. Foren. Bd. 69. 21 
