20 



by the flabellse, passes the above-named triangular space. At other times almost all 

 material is swallowed. 



Behind the sharp transverse ridge to which the maxillae are attached we find 

 the mental and labial structures. Mesially are found four chitinous structures, ac- 

 counted for by RASCHKE (1887 p. 10) and MEINERT (1886 Tab. I. fig. 5) and men- 

 tioned in all works on mosquito larvae: 1. a delicate, roughly triangular plate with 

 a marginal hair-fringe and protruded into along tooth at the middle. 2. behind this 

 the mental sclerite, a heavily chitinised, dark, roughly triangular dentate plate. 

 3. behind this a complicated plate with teeth and spine-like structures, commonly 

 regarded as labium and. 4. at the margin of the pharynx the hypopharynx, a simple 

 chitinous cone (Howard, Dyar and Knab I. p. 87). 



Of these organs No. 2, the mental sclerite or mentum, is very conspicuous; it is 

 commonly triangular, on its apex provided with a rather conspicuous thorn and with 

 the sides bordered by a number of shorter spines ; the form of the mentum and the 

 number of lateral spines have some significance as a means of classification; and are 

 therefore often mentioned in systematical descriptions. The Danish species of the 

 Genus Culex may always be distinguished by means of its high form of the men- 

 tum with rectangular sides; T. annulata by its many small lateral teeth, and 

 Tceniorhynchus by its very few large ones; in the genus Ochlerotatus it is triangular 

 with about from ten to fifteen small teeth; as far as I can see, it cannot be used 

 to distinguish the species of this genus from each other. Beneath the mentum is found 

 the very peculiar organ (3) which has been figured by MEINERT (1886 PI. I. fig. 5) 

 and better by RASCHKE (1887 fig. 13. Tab. VI) but never thoroughly described; it 

 consists of a tube, probably provided with a central pore. It is surrounded by a collar- 

 like part, consisting of plates of chitin which overlap each other and are furnished 

 with teeth along the edges. The organ rests upon a dome-like body, supported by 

 two lists of chitin, and inwardly provided with a thorn-like process. Thorns of 

 chitin are also present on the dome-like part. Meinert's drawing exhibits a circle 

 of hairs rising from the apex of the tube; when cut horizontally, the organ shows 

 a cushion-like layer of cells with large nuclei beneath the dome-like part. Two 

 divergent muscles run to the organ, serving to push it forward and to retract it. Its 

 appearance differs but little within the different Culicin larvae. 



How these four above-named different parts act, I do not know; I have never 

 during the feeding process seen the mentum carry out any movement; the tube 

 with the collar-like expansion lies directly at the entrance to the pharynx; I sup- 

 pose it has a secretory function. The above-named pellets which leave the tri- 

 angular space between the maxillae during the movements of the flabellae, are wrapped 

 up in a mucous substance, and I suppose that it comes from the above-named 

 pore. Further I call attention to some peculiar movements of the larva, easily 

 to be observed and often figured in old as well as in new literature. When the 

 larvae are hanging down from the surface, we often see them release their hold; 

 the body is bent, and the apex of the sipho is put into the mouth. In this position 



