38 



are obscured by the dark color cf the insect's back. Occasionally too 

 large a fragment to be swallowed with ease clogs the mouth. Some- 

 times it enters the mouth and sticks. In such cases the head of the 

 larva revolves with lightning-like rapidity and the fragment is nearly 

 always disgorged, although sometimes it is swallowed with an evident 

 effort. Since the Anopheles larva feeds only upon these light floating 

 particles, its specific gravity is nearly that of the water itself and it 

 supports this horizontal position just beneath the surface film with 

 comparative ease, and in fact without efl'ort, the tension of the surface 

 __ film itself being 



hardly needed to 

 hold it. It requires 

 an effort in fact for 

 the Anopheles larva 

 to descend (which it 

 apparently never 

 does up to the period 

 of the final larval 

 stage, except when 

 alarmed), while it 

 requires an effort 

 for the Culex larva 

 to ascend. 



Structurally the 

 differences between 

 the half-grown 

 larv83 of Culex and 

 Anopheles are well 

 shown at figs. 13, 14, 

 and 15. The great 

 size of the head of 

 Culex, as contrasted 

 with the small head 

 of Anopheles is a 

 most striking differ- 

 ence. The very 

 long respiratory 

 siphon (as Miall calls it) of Culex contrasts markedly with the short 

 one of Anopheles. The arrangement of the hairs is entirely different, 

 the branching of the hairs of Anopheles, as contrasted with the simple 

 hairs of Culex and the little paired star-shaped (apparently branchial) 

 tufts on the dorsum of Anopheles are entirely absent with Culex. The 

 flaps at the tail end of the body are similar in number, but are held in 

 a somewhat different position. 



Fig. 14.— Figure at top, half grown larva of Anopheles in feeding posi- 

 tion, just beneath surface film. Figure at bottom, half grown larva 

 of Culex in breathing position — greatly enlarged (original). 



