II 



FLIES WITH AQUATIC 



125 



There is a pair of strong, toothed mandibles, which 

 are the chief organs of mastication. The maxillae 

 are rudimentary, and the labium is represented by a 

 crescentic plate with strongly toothed fore-edge. 



The transparency of the Chironomus larva is suffi- 

 cient to permit the study of its internal organs in a 

 living and uninjured specimen. Small larvae, say one- 

 quarter of an inch long, are best for the purpose. It 

 is a good plan to make a little cell of cotton wool or 



c 



FIG. 38. Larva of Chironomus. A, head, dorsal side ; B, head, front view ; C, edge 

 of labium, with peculiar teeth and papillae. 



silk upon a microscopic slide, to fill this with water, 

 place the larva in it by means of a fine brush, and 

 then gently lower the cover-glass. The imprisoned 

 larva can thus be studied microscopically. All the 

 external organs, the nervous system, the alimentary 

 canal, and the heart can easily be made out, and the 

 action of the jaws can be studied. 



The alimentary canal begins with a long, narrow 

 oesophagus. This is telescoped behind into the crop 

 or proventriculus, which is of much greater diameter 



