144 



ENTOMOLOGY FOR MEDICAL OFFICEBS 



false longitudinal vein is nearly always present and is a 

 characteristic feature. The head is sometimes elongated in 

 the neighbourhood of the mouth, like a proboscis. The 

 larvae of certain species are aquatic, and have at the 

 posterior end of the body (Fig. 48) a long breathing-tube 



Fia. 4S.— Bat-tailed larya of Bristalis. 



which can be lengthened or shortened like a telescope to 

 suit the depth of the water in which the larva finds itself 

 These larvae, which are known as " rat-tailed larvae," live in 

 foul water ; they are sometimes found in wells and occasion- 

 ally have been ingested by human beings and subsequently 

 passed by the bowel. 



Family Phorid^. (This family is sometimes classed 

 with the Brachycerous Orthorrapha. In some of the species 



Fio. 49. — Antenna of A^noQhKta 

 fcrruginca : the very much- 

 enlarged lower figure in longi- 

 tudinal section. 



Fill. 50. — Apiochceta femi^n^a. 



the wings are much reduced in size, and in a few they are 

 absent altogether.) The PhoridcB are small flies with 

 humped back; strong, usually bristly, legs; and peculiar 

 antennae and wings. In the antennas (Fig. 49) the 3rd 



