xxiii INSECTA : DIPTERA 341 



part of the lower lip, though higher up this separates 

 from the lancets and bends backwards as they enter the 

 skin, and so the distance between this and the gnat's head 

 is lessened. 



The blood is drawn up by the suction caused by the 

 dilatation of part of the oesophagus. The gnat not only 

 pierces the skin and sucks up the blood of its victim, but 

 is said also to inject into the wound a poisonous fluid which 

 causes irritation and inflammation no poison-gland, however, 

 has yet been demonstrated. 



The male gnat has a similar proboscis, but it contains 

 two pairs of simple unserrated lancets only ; also there is no 

 similar power of suction in the oesophagus, and it is doubtful 

 whether he ever stings. 



The buzzing of a gnat is caused in two ways : 

 ^ ne deeper notes, by the vibration of the wings in 

 flying; the shriller notes, by the vibration of 

 minute stiff membranes, placed just behind the spiracles 

 which occur in a row down each side of the body. The 

 shrill buzzing seems to be confined to the female gnat, and 

 serves to attract the males ; their bushy antennae have been 

 shown to be thrown, by this special pitch of note, into 

 sympathetic vibration, and swarms of them can be attracted 

 by sounding this note artificially. 



After mating, the female fly makes her way to 

 water, in a ditch or rain-water tub perhaps, and 

 there she lays her eggs on the surface, two or three hundred 

 of them. As they are laid, 

 she arranges them with her 

 hind legs and glues them 

 together, side by side, mak- 

 ing a little floating " raft " 

 of eggs (Fig. 262): these 



arP all nofnted at their FIG. 262.-The Gnat jjpw 

 are all pointed at their R a ft of Eggs floating in the water, 

 upper end, and between 

 the points a bubble of air is securely held, so that if the 

 raft is submerged or upset, it always floats to the surface 

 and rights itself again. This is of importance, since the eggs 

 require plenty of air for their development. After two or 

 three days, the eggs hatch, the lower end of each separating 

 off neatly as a little hinged lid (Fig. 263). 



