INSECTA : DIPTERA 345 



The Larva ^ arva (Fig- 266) grows to about half an 



inch in length, and is transparent for the most 

 part, so that when motionless it is quite difficult to distinguish, 

 the only noticeable parts of the body being the dark eye-spots 



aJr sax 



. 

 Vnx: 'mnd- 



FIG. 266. Corethra plumicornis (the "Phantom larva "). 

 mm?, Mandible ; mx, maxilla ; ant, antennae. 



on the head, and the air-sacs with their dark pigment on the 

 thorax and on the seventh abdominal segment. When dis- 

 turbed, the larva moves with great rapidity, nicking its tail 

 and then quickly becoming once more motionless. The 

 movement is aided by the vertical fin of stiff plumed hairs which 

 is attached below the tail segment of the body, and corresponds 

 to the vertical fin in the gnat larva. 



This "phantom" feeds on any minute larvae 



Larva or crus taceans in the water, seizing them with its 



antennae, which are modified for this prehensile 



function, and then crushing them and passing them into the 



mouth with its strong toothed mandibles, the maxillae and 



labium also helping in the process. 



Professor Miall tells us that this solid food passes into 

 the mouth but no further, the back of the mouth being closed 

 by a fringe of stiff hairs. The food, therefore, is dissolved by 

 the secretions of the mouth, and only the liquid portion 

 passes on into the stomach, the insoluble particles being 

 expelled from the mouth by the eversion of the pharynx. 



Respiration seems to take place through the 

 wllole sur ^ ace of tne body, for tner e are no 

 spiracles. The two pairs of air-sacs, which are 

 enlargements of the two air- tubes of the body, alone, of all 

 the tracheal system, contain air, and their surface is marked 

 by spots of black pigment, which, it is suggested, may have 

 something to do with the chemical process by which these 

 air-sacs, empty in the young larva, are filled later. Doubtless 

 the sacs function as floats to support the body. 



