17 



tides from the decaying leaves, using this material as food. It is a very common 

 phenomenon to see these larvae sink down to the bottom and, in an oblique posi- 

 tion, with the hair-brushes expanded and pressed down to the substratum, steadily 

 move over the leaves or along the sides of the aquaria. It is a remarkable fact 

 that these two types of hair-brushes and the very different mode of getting food in 

 the mosquito larvae have hitherto been quite overlooked. It is the last-named form 

 of the flabellae which we mainly find in Ochlerotatus. 



The hairs of the labrum as well as the short hairs on the palatum have prob- 

 ably also quite another function ; they pay the double debt as organs of nutriment and 

 of locomotion. Undisturbed most Culex larvae hang down from the surface with the apex 

 of the sipho supported by the surface film, and with the flabellae whirling water 

 currents into the mouth-parts. Apart from the flabellse the body is motionless. Sud- 

 denly we see the larvae, with the apex of the sipho in the surface, move slowly 

 forward. In quite the same way we see the larvae which seek their food, either on 

 the sides of the aquaria or at the bottom, suddenly stand still, and suddenly, but 

 slowly, move forward, the flabellae being pressed down against the substratum. 

 Many of the species are also able to move slowly forward in a peculiarly sliding 

 manner in a horizontal direction in the free watermasses, stand still for a moment 

 and then move onward again. Otherwise the free watermasses are commonly not 

 the home of the mosquito larvae; they are only traversed when the larvae is to go 

 from the bottom to the surface or vice versa. The way is traversed either actively 

 by means of wriggling of the abdomen and of the swimming brushes or passively 

 (see later) ; the active motion is mainly in a vertical direction with the head turned 

 away and the tail in the direction of the locomotion; it is generally very rapid. 



Now I have often thought that the above-named sliding motions were produced 

 by the brushes of the last abdominal segment, but studying the organ in living larvae 

 under the binoculary aquarium microscope I have convinced myself that this 

 locomotion is not produced by these organs. At all events the tail and its hairs are 

 held quite motionless. There is therefore no other possibility but that the move- 

 ments are due to the flabellae. To me there is only this great difficulty that it is quite 

 impossible to see why the organs, though almost always in constant motion, in some 

 moments produce a motion of the whole body and in others, though still moved, 

 produce not even the slightest movement of the body. I have tried with my 

 best microscopes to study this in living animals, but I have been quite unable 

 to see what the larva prepares to do, when it suddenly applies the organ to be 

 used in the service of locomotion. I only feel convinced that it is not the hair- 

 fringes on the mouth-parts which are used; it is the hairs of the flabellae, which 

 are suddenly either moved faster, or struck out in another direction. In the first year 

 while I was always studying C. morsitans, which commonly in the autumn hangs 

 down from the surface, I thought for a long time that the larva was in some way 

 glued to the surface by the apex of the sipho and, without altering the use of 

 the flabellae, only moved when the agglutination ceased. Later on, when studying 



D. K. D. Vidensk. Selsk. Skr., naturvidensk. og raathem. Afd. 8. Rsekke, VII, 1. 3 



