II FLIES WITH AQUATIC LARV.E 211 



bars, which in some places pass into teeth, stand out 

 from the ridges. How the plates are employed has 

 not been discovered. They cannot be protruded from 

 the mouth. 



" Just in front of the pharyngeal fringes, and in the 

 floor of the passage, is a transverse row of backward- 

 directed setae.^ 



" Batelli aptly compares the action of the fringes 

 to that of the strainers of the Baleen Whales." 



The larvae feed upon organic matter, decaying 

 leaves, &c., found in stagnant water. Reaumur found 

 that when kept in clean water and supplied with 

 bread, they lived until they had completed the larval 

 stage. 



When the time for pupation comes the Rat-tailed 

 Maggot quits the water. Its body becomes encrusted 

 with earthy particles which adhere in consequence of 

 the sticky exudation from the skin. When placed 

 on damp loose earth, they enter it and undergo their 

 transformation beneath the surface. For convenience 

 of observation Reaumur kept some larvae which were 

 ready to change in empty boxes. They glued them- 

 selves to the wood, and if only slightly attached by 

 the hinder part of the body, the transformation was 

 successfully effected ; but when the whole of the 

 under side stuck to the wood, the larva perished. 



These Insects, like the Blow-fly and Stratiomys 

 form a cocoon out of the larval skin. The colour 

 changes from white to yellow ; the tail becomes 



' In the larva of the Blow-fly the sensory papilte, the shell- 

 like plates and the pharyngeal strainer or its equivalent can be 

 observed. See Lowne on the Blow-fly, 2nd ed., Figs. 5 and' 8. 



V 2 



