The Larva of " G2ilex " and " Anopheles' 



in larva? of the genus Stegomyia the siphon tube is very short and 

 thick, and in those of the genus Culex it is long and thin. Ste- 

 phens and Christophers employ the term " siphoriic index " for the 

 figure obtained by dividing the length of the siphon tube by its 

 greatest breadth, and state that for the different species in any 

 genus this figure is very constant. In Stegomyia larvae, for ex- 

 ample, the siphonic index is about 2, i.e., the length of the tube is 

 about double its greatest breadth, in Culex larva? it is about 4, and 

 in Tceniorhynchus larvae it may be as much as 13. 



The ninth abdominal segment is cylindrical in shape and carries 

 the opening of the anus, around which are symmetrically arranged 

 the four anal papilla?. On the dorso-lateral surface of certain of the 

 abdominal segments of " anopheles " larva? characteristic structures 

 called " Palmate hairs " are present (see PI. IV). Each of these 

 hairs has a short stalk, to the apex of which are jointed a number 

 of leaflets, which, when spread out, are arranged somewhat like 

 the ribs of an umbrella which has been turned slightly inside out, 

 or perhaps more nearly like the leaf of a cocoanut palm. Two of 

 these palmate hairs are present on each segment which is provided 

 with them, and it is chiefly by their means that the larva main- 

 tains its position close under the surface of the water. They are 

 not present on the larvae of any other kind of mosquito than 

 " anopheles." 



On account of their presence and on account of the absence of 

 a siphon tube " anopheles " larva? float in the water immediately 

 beneath and parallel with the surface film ( PL II, Fig. 2). 



On account of the presence of a siphon tube and the absence 

 of palmate hairs " culex " larva? float considerably below and at an 

 angle with the surface film (PI. II, Fig. 1 ). 



These are the essential differences by which " anopheles " and 

 " culex " larva? may be distinguished from each other, and it is un- 

 necessary to describe in detail the differences between any other 

 regions of the larva? of these two kinds of mosquitoes. The head of 

 an " anopheles " larva (PI. IV) is more or less rounded in shape 

 and is covered by a clearly defined chitinous case. The eyes are 

 situated laterally, and in front of each eye is an eminence which 

 carries the antenna. A broad band of pigment runs across the 

 head between the two eminences from which the antenna? arise, and 



[9 



