LIFE-HISTORY OF THE GNAT 251 



globular anterior mass (the head and thorax), and of 

 a flexible abdomen. Unlike the larva, however, it 

 now comes to rest at the surface-film with the globular 

 head upwards and the tail downwards. This change 

 in position is significant, and is effected by two hairy 

 horns or minute trumpets that project from the back 



FIG. 53. The pupa of the common gnat in its characteristic attitude. The 

 respiratory trumpets (S) maintain a hold on the surface-film of the 

 water. The wings (W), legs, antennae, and mouth-parts can be seen. 

 Of the mouth-parts Lib is the large upper lip, MX and Map the lower 

 lip. Tib } refers to the first leg ; Tib.,, to the second legs, the third 

 is seen under the wing. (Ajter Hurst.} 



of the thorax. These are now the outlet and inlet 

 of. the tracheal system. The hairs lining them 

 suspend the body by the tension of the surface-film, 

 whilst a stroke or two of the tail, aided by the tail-fin, 

 severs this hold and carries the pupa downwards, 



