A. D. Imms 
123 
(2) The Gidex type, in which the spiracles are situated at the 
extremity of a siphon formed as a drawing out or prolongation of the 
dorsal region of the eighth abdominal segment. The two main 
longitudinal tracheal trunks are usually of a much greater diameter 
than in the Anopheles type, and apparently function to some extent as 
“air reservoirs.” There are no palmate hairs, and the comb almost 
always consists of a variable number of scale-like spines. 
(3) The Sayomyia type is, on the whole, the most modified among 
the Culicidae. The spiracles and respiratory tube are absent and the 
tracheal system is greatly reduced and mainly consists of two pairs of 
air vesicles which are situated respectively in the thorax and seventh 
abdominal segment. 
Theobald (1905) recognises eight sub-families among the Culicidae 
viz. the Anophelinae, Megarhininae, Toxorhynchitinae, Culicinae, 
Joblotinae, Aedomyinae, Heptaphlebomyinae and Corethrinae. 
The Anophelinae form a tolerably natural group and exhibit a 
great similarity among their larvae. The most obvious differences 
that are to be found are seen in the characters of the frontal, plumose, 
and palmate hairs, the antennae, the form of the comb and the labial 
plate. 
The Megarhininae comprise the single genus Megarhinus. The 
larva is of the Gulex type, but is remarkable in having the comb 
represented by a large chitinous plate and in the pecten being absent. 
It is said to possess a rudimentary spiracle on the last abdominal 
segment (Felt, 1905, p. 445). The larva of Toxorhynchites very closely 
resembles that of Megarhinus and it has been pointed out by 
Christophers (1906, p. 13) that they agree very closely in the shape of 
the head and clypeus, in having the brushes modified into “clasping 
organs ” for seizing their prey and in the anal gills being reduced to 
stump-like papillae. 
In T. immisericors (Walk.) according to Theobald (vol. iii. p. 118) 
and Green (1905, p. 159) the siphon is excessively short, and there are 
no anal gills and the larva rests very nearly parallel to the surface 
film. 
The Culicinae exhibit a wide range of variation in their larval 
structure. The most striking and variable organ is the siphon which 
differs greatly in its length and general shape among various genera. 
Stephens and Christophers obtain what they term the “siphonic index” 
by dividing the length of the tube by its maximum breadth. This 
index is useful for comparative purposes and appears, on the whole, to 
