DIPTERA. 483 



of low grounds and water, where they are most abundant, is well known. 

 These Insects also feed on the nectar of flowers. 



The female deposits her eggs on the surface of the water, and places them 

 side by side in a perpendicular direction; the entire mass resembles a little 

 bateau floating on that element. Each female lays about three hundred 

 eggs in the course of the year. These Insects frequently survive the most 

 intense cold. Their larvae swarm in the green and stagnant waters of ponds 

 and ditches, particularly in spring, the period at which those females lay 

 their eggs who have passed through the winter. They suspend themselves 

 on the surface of the water in order to respire, with their head downwards. 

 These larvse are very lively, swim with considerable velocity, and dive from 

 time to time, but soon return to the surface. After some changes of tegu- 

 ment, they then become nymphs, which still continue to move by means 

 of their tail and its two terminal fins. These nymphs also remain on the 

 surface of the water, but in a different position from that of the larvae, their 

 respiratory organs being placed on the thorax; they consist of two tubular 

 horns. It is in the water also that the perfect Insect is developed. Its 

 exuviae form a sort of float or resting place, which keeps it from submer- 

 sion. All these metamorphoses occur in the space of three or four weeks, 

 and several generations are produced in the course of the year. 



In the other Nemocera, the proboscis is either very short and 

 terminated by two large lips, or in the form of a siphon or rostrum, 

 but directed perpendicularly or curved on the pectus. The palpi 

 are bent underneath, or turned up, but in that case, from one to 

 two joints only. 



Linnaeus comprises them in his genus 



TIPULA. 



Which is now variously divided and subdivided. It includes the various 

 species of the Crane-fly. 



All the following Diptera, a small number excepted, have their 

 antennas composed of three joints, the first of which is so short, that 

 it may be excluded from the supputation; the last isannulated trans- 

 versely, but without distinct divisions. It is frequently accompanied 

 with a seta, usually lateral, and situated on the summit in others 

 presenting two joints at base, sometimes simple and sometimes silky 

 The palpi never have more than two joints. 



Some, a few excepted, whose larvas divest themselves of their 

 skin previous to becoming pupa?, always have a sucker composed 

 of six or four pieces; the proboscis, or at least its extremity, that is 

 to say, its lips, is always salient. The palpi, when they exist, are 



