11 



FLIES WITH AQUATIC LARV^ 



115 



»y 



^'m 



i\\\i', 



fetching up mud from the bottom of a deep ditch or 



pool, the hoop and gauze 



may be used without the 



muslin. Another implement 



which is worth carrying is 



a large iron spoon with a 



long handle. 



The Corethra larva feeds 

 upon small aquatic animals, 

 such as Ephemera-larvae, 

 iJaphnia, or Cypris. The 

 transparency of its body and 

 its immobility, except when 

 it instantaneously changes 

 its position, enable the larva 

 to wait for its victims with- 

 out risk of being observed. 

 Limbs would be here super- 

 fluous, and nothing can be 

 seen of them except a pro- 

 minence provided with a 

 double crown of minute 

 teeth, which can be distin- 

 guished by the microscope, 

 at the extreme end of the 

 tail. This represents, in a 

 greatly reduced form, the 

 pair of hooked feet found at 

 the hinder end of the body 

 in Chironomus and Tanypus. 

 A little farther in front, on 

 the lower surface of the body, is a vertical fin, 



I 2 



Wl 



m 



Fig. 31. — Larva of Corethra. A, 

 dorsal view. B, side view. X 8. 

 The two pairs of air-sacs are seen 

 in the first and eighth segments 

 behind the head. 



