XXIII INSECTA. DIPTERA 345 



_. - The larva (Fig. 266) grows to about half an 



inch in length, and is transparent for the most 



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



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



ziir sac 



Itix: "mnd- 



Fig. 266. — Corethra pliimicornis (the "Phantom larva"). 

 m)«i, 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 larA'a moves with great rapidity, flicking its tail 

 and then quickly becoming once more motionless. The 

 movement is aided by the vertical fin of stifi^ 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 

 La ^^ crustaceans 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 

 Eespiration .j^jjgjg surface of the body, for there 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. 



