744 CLASS IV. INSEOTA. 



protuberance which diverges dorsally from the penultimate segment, and 

 so gives a Y-shaped appearance to the larva, whose body hangs down into 

 the water (Fig. 475). The larva of Anopheles lies flat beneath the surface- 



c a 



d 



FIG. 477. Pupa of Anopheles macuUpennis attached to the surface-film of water, magnified 

 (after Nuttall and Shipley), a breathing trumpet ; 6 eye ; c palmate hairs on the anterior 

 end of the abdomen which clings to the surface-film ; d antennae. 



film, attached to it by paired palmate hairs and by the saucer-like opening of 

 the two stigmata (Fig. 476). The pupae also hang on to the surface-film and 

 breathe through two trumpet-like stigmata situated behind the head (Fig. 

 477). The larva of Corethra has no stigmata. The images are peculiar 

 amongst Diptera in the possession of scales both on the body and on the 

 wings. Gnats often occur in quite incredible numbers, dancing in the 

 air in dense clouds. The images frequently live through the winter hidden 

 away in obscure outhouses and corners : the eggs and also the larvae 

 survive the cold of winter. Lately this family has attracted much atten- 

 tion, as it has been shown that Anopheles maculipennis, a widely dis- 

 tributed species, common in Britain, is the distributing agent (with other 

 species) of the Haematozoon which causes malaria ; and is also, together 

 with Culex, the distributer of certain Filarias which cause various disorders 

 in tropical countries (vol. 1, p. 289} ; whilst Stegomyia fasciata, a common 

 gnat, plays a similar role in the case of Yellow-fever.* Other genera are 

 Aedes, Megarliinus, and Psorophora. 



Fam. 5. Chironomidae. Small flies with narrow wings, and no projecting 

 rostrum. Long antennae, plume-like in male, and long legs. Xo ocelli. 

 This family includes forms popularly termed gnats and midges. It com- 

 prises a large number of species and is universally distributed. Like the 

 Culicidae the species frequently form dense, dancing swarms. Their larvae 

 are aquatic, without stigmata ; and often blood-red from the presence of 

 haemoglobin ; hence their name of blood-worms. They often form tubes 

 of mud or sand. A few are marine. Chironomus is said to have some two 

 hundred British species. Ceratopogon is the midge which causes much 



* The disease-conveying gnats play so large a part in human economy 



