22 NOKTII AMERICAN DIPTEEA. 



that brings little });a-ti('les of food Avithin reach of the mouth. 

 After changing their skin two or three times they assume a 

 more club-shai)ed appearance, in which the parts of the adult 

 insect are indistinctly seen. The abdomen terminates in two 

 leaf-like appendages that act as propellers ; but in general 

 these pupaj remain near the surface, except when disturbed, 

 and take no food. Tlie breathing organs are no longer a tube 

 at the tip, but there are now two that spring from the sides of 

 the thoracic segments. Finally when the perfect mosquito is 

 ready to emerge from the pupa, the back of the skin, wliicli 

 has now come to the surface and is exposed, splits, and the tiy 

 carefully and gradually extricates itself from the membrane 

 which thus serves the place of a raft till the legs and wings 

 are sufficiently firm. But right now is the period of the mos- 

 quito's life most fraught with danger ; a wavelet, a breath of 

 air, or a raindrop, hopelessly shipwrecks the frail bark. This 

 is why running waters are free from these insects. 



TABLE OF GENERA. 



1. Proboscis sliort, not longer tlian tlie liead ; metatarsi longer tlian tlie fol- 



lowing joint. CoKETHRA Meigen. 



Proboscis much elongated, longer than the head and thorax together. 2 



2. Proboscis strongly curved, palpi of the male very long, of the female 



short. ..... 



Proboscis straight. ..." 



■J. I'alpi in both sexes of equal length. 

 Palpi in the male long, short in female. 



4. Palpi longer than the antenna;. 

 Palpi shorter tiiaii the antenna;. 



Megaruiiinus Kob. llesv. 



4 



. CuLEX Linne. 



AxopnEi.KS Meigen. 

 ^EoKS Meigt'U. 



5. CHIPvONOMID^. 



Gnatlike flies of slender form, the males conspicuous for 

 their ])lumose antenme, seldom reaching ten millimeters in 

 length. Head small, spheroidal, more or less concealed by a 

 projecting, hoodlike thorax. Antenntp threadlike or beadlike. 



