466 DIPTERA CHAP. 



pupa are really each four-leaved. The pupa is formed within 

 the larval skin, but the latter is subsequently cast so that the 

 pupa is exposed ; its dorsal region is horny, but the under sur- 

 face, by which it clings firmly to the stones of the rapid brook, is 

 white and scarcely chitinised, and Dewitz considers that the 

 chitinous exudation from this part is used as a means of fastening 

 the pupa to the stones. Blepharoceridae possess, in common 

 with Gulex, Psychoda and Ptychoptera, the peculiar number of 

 five Malpighian tubes, and it has been proposed by Miiller to 

 form these Insects into a group called Pentanephria. 



Fam. 4. Culicidae (Mosquitoes, Gnats). Antennae with whorls 

 of hair or plumes, which may be very dense and long in the male, 

 though scanty in the female ; head with a long, projecting pro- 

 boscis. Although there are few Insects more often referred to 

 in general literature than Mosquitoes, yet the ideas in vogue 

 about them are of the vaguest character. The following are the 

 chief points to be borne in mind as to the prevalence of Mos- 

 quitoes : The gently humming Gnat that settles on us in our 

 apartments, and then bites us, is a Mosquito ; there are a large 

 number of species of Mosquitoes ; in some countries many in one 

 locality ; in Britain we have ten or a dozen ; notwithstanding the 

 multiplicity of species, certain Mosquitoes are very widely diffused ; 

 the larvae are all aquatic, and specially frequent stagnant or 

 quiet pools ; they are probably diffused by means of the water 

 in ships, it being known that Mosquitoes were introduced for 

 the first time to the Hawaiian Islands by a sailing vessel about 

 the year 1828. Hence it is impossible to say what species the 

 Mosquitoes of a given locality may be without a critical examina- 

 tion. No satisfactory work on the Mosquitoes of the world 

 exists. Urich states that he is acquainted with at least ten 

 species in Trinidad. The species common in our apartments in 

 Central and Southern England is Culex pipiens, Linn., and this 

 species is very widely distributed, being indeed one of the 

 troublesome Mosquitoes of East India. The term Mosquito is a 

 Spanish or Portuguese diminutive of Mosca. It is applied to a 

 variety of small flies of other families than Culicidae, but should 

 be restricted to these latter. The irritation occasioned by the 

 bites of Mosquitoes varies according to several circumstances, 

 viz. the condition of the biter, the condition or constitution of 

 the bitten, and also the species of Mosquito. Keaumur and 



