CULEX. INSECTS. 375 



not well ascertained. In many species above these balancers are found two appen- 

 dages of a papyraceous consistence, generally white or yellowish, and resembling the 

 valves of shells, attached together by one of their sides. One of these pieces is at- 

 tached to the wings and participates in their movements. These appendages often 

 conceal the balancers. The larvae of the Diptera have no feet ; but in some are 

 found appendages which contribute to locomotion. Their mouth is generally furnish- 

 ed with two hooks. The orifices for respiration are principally at the posterior ex- 

 tremity of the body. Many of the insects of this order, such as the gnats and gad- 

 flies, are troublesome from their bite, and torment many of the domesticated animals. 

 Others, as the (Estri, deposit their ova on the bodies of animals, upon which their 

 larvse feed. And some, in localities where they are exceedingly multiplied, destroy 

 in this manner the young plants of the Cerealiae, and often annihilate the hopes of 

 the husbandman. The duration of life in the Diptera is not long, in the perfect 

 state being limited to a few weeks or months. All undergo a complete metamor- 

 phosis, but modified in two principal ways ; some forming a cocoon, while in others 

 the skin of the larvae hardening becomes a solid covering, of an oval form, like a 

 grain of seed or an egg, and presenting no exterior marks of the contained animal. 



SECTION I. 



Head always distinct from the thorax, large, or medium sized ; 

 hooks of the tarsi simple or unidentated ; sucker inclosed in 

 a sheath ; larvae with the body, and the cocoon, when it is 

 formed of the skin, always annulated through its whole length. 



FAMILY I. NEMOCERA, Lat. 



Antennae composed at least of six joints ; but generally from 

 fourteen to sixteen ; the larvae with a scaly head, and chang- 

 ing their skin to pass into the pupa state. 



The insects of this family, which composed the genera Culex and Tipula of Lin- 

 naeus, have an elongated body ; the head small and rounded ; the eyes large ; the 

 antennae filiform or setaceous, longer than the head, often hairy ; the trunk projec- 

 ting, either prolonged in the form of a syphon or beak, or short, and terminated by 

 two large lips ; two exterior filiform or setaceous palpi, generally composed of five 

 joints ; the thorax thick, elevated, and gibbous ; the wings oblong, and the balancers 

 discovered ; the abdomen elongated, commonly of nine rings, pointed in the females, 

 and with forceps or hooks in the males ; feet long and slender. Many of the smal- 

 ler species assemble in numerous troops, and form airy dances while flying- 



TRIBE I. CULICIDES. 



Trunk cylindrical, long, projecting, tumid at the end, and in- 

 closing a sucker of six pieces ; palpi directed forwards, and 

 very hairy, at least in the males ; antennae filiform, the length 

 of the head and thorax, of fourteen joints, plumose in the 

 males ; eyes lunate ; wings close to the body, with longitu- 

 dinal scaly nerves ; legs long. 



The larvae are aquatic, and lose not the faculty of moving and swimming after 

 having passed into the pupa state. 



I. Palpi of the males, or both sexes, at least as long as the trunk. 



Gen. CULEX, ANOPHELES. 



II. Palpi short in both sexes. 



Gen. ^EDES. 



Gen. CULEX, Lin. Lat. 



Antennae setaceous, of about fourteen joints, furnished with 

 hairs, which form a tuft in the males ; rostrum long, inclos- 



