II FLIES WITH AQUATIC LARV^ 191 



be described later on, against the attacks of predatory 

 animals. The colour is in some degree protective, 

 consisting of shades of green, brown, and yellow, and 

 exhibiting an irregular pattern of spots and streaks. 

 Stagnant waters of small extent, and especially 

 ditches, are its favourite haunts. The larva of 

 Odontomyia, which is very similar to that of Stra- 

 tiomys, prefers the shelter of Duckweed and other 

 aquatic plants. Stratiomys occurs in various parts of 

 England, but is reputed rather rare, perhaps because 

 so little attention has been paid by English naturalists 

 to aquatic Diptera. 



The head of the larva is greatly reduced, and con- 

 sists of a middle part, black, horny and pointed, which 

 is separated by deep clefts from the lateral parts. In 

 these clefts lie the palps, which bear strong hairs. A 

 number of hooks arm the mouth. The food consists 

 of microscopic organisms swept into the mouth by 

 the palps. 



The extremity of the tail forms a beautiful coronet 

 of branched filaments, about thirty in number, which 

 are accessory to respiration. When this coronet is 

 expanded it forms a basin open to the air and im- 

 pervious to water, by reason of the fineness of the 

 meshes between the component filaments. Were the 

 larva provided with a basin of the same proportions 

 formed out of continuous membrane it might float 

 and breathe perfectly well, but would find it hard 

 to free itself neatly and quickly from the surface-film 

 when some sudden emergency rendered it necessary to 

 descend. As it is, the plumed filaments collapse and 

 their points approach ; the side branches are folded 



