14 



off and arranged vertically on the slide, so that it is possible to look directly down- 

 wards at the apex of the sipho. This is a very difficult process. 



The sipho carries hairs and thorns in different arrangement. On the basal third 

 of the sipho are inserted two ventro-lateral series of spines, commonly determined 

 as pecten. This organ is of great value for classification. It commonly consists of 

 from twenty to thirty strongly chitinized spines, arranged on a line and at almost the 

 same distance from each other; at the base they are dentated, carrying from one 

 to six teeth; they may be flattened as is the case with F. geniculata, C. morsitans, C. 

 pipiens and nigritulus, formed here as oblique feathered scales of brighter, almost 

 yellowish chitin. In Theobaldia annulata we find no thorns, but only a series of 

 long soft hairs, without any teeth at the base. In some species the last thorns, 

 those nearest to the apex of the sipho, are at a larger distance from each other than 

 the following; they are not dentated and often inserted out of line (Aedes cinereus, 

 0. diantceus, 0. lutescens, excrucians, diversus, prodotes). The position of these spines 

 varies from species to species. In Tceniorhyncus the pecten is wanting (see remarks 

 later on). Also the function of this organ is quite enigmatical. It differs from 

 species to species; that it should have no significance whatever I regard as highly 

 improbable. It has so great a similarity to a comb that it must be regarded as fairly 

 probable that it may be used as an organ, by means of which the different hair-tufts 

 may be cleaned. The hair-tufts of the sipho present some of the best structures 

 for purposes of classification we have hitherto been able to find in the Culicin larvae. 

 According to the drawings published by HOWARD, DYAR and KNAB the tufts may be 

 arranged very differently from what I have seen in the relatively poor Danish fauna; 

 for a more thorough study I refer the reader to the above-named tables. In the Danish 

 larvae the most constant tuft is the apical one, very near the apical end of the pecten. 

 It consists of from five to seven feathered bristles. It may, as in 0. annulipes, lutescens 

 and excrusians, be highly developed or, as in Aedes, be rather inconspicuous ; it may 

 be wholly absent, but we then find another, equally well developed, brush at the basal 

 end of the pecten (Theobaldia annulata, C. morsitans). In Culex pipiens and C. nigri- 

 tulus we find four or five tufts with two hairs generally arranged serially and 

 ventrally, but with one or two of the tufts out of line. Only in 0. rusticus four 

 tufts of double hairs are inserted on the dorsal side of the air tube, opposite to 

 the pecten. Dorsally near the apex is further inserted a short thorn; two of the 

 flaps carry two short curved spines which are often used when the larvae rest on 

 the bottom with the dorsal face downwards, or when they are hanging from or 

 supported by waterplants. With regard to the modifications of the eighth segment 

 of Tceniorhynchus I refer to my paper (W.-L. 1918 p. 277). 



The ninth segment or Anal Segment is out of plane and inserted upon the 

 eighth segment. It is short, often almost isodiametrical, in F. geniculata shorter 

 than broad, in Tceniorhynchus twice as long as broad. It is covered with a chiti- 

 nous plate, short in the larva of the first stage, but in the fullgrown larva often 

 rounding the whole segment, but mostly only covering about two-thirds of it. At 



