HOUSE FLIES AND BLUEBOTTLES 179 



somewhat in different genera or even species, but is con- 

 stant in the same, and the general plan is sufficiently 

 definite to permit of the individual nervures being identi- 

 fied and named, so as to be used as aids in classification. 

 A comparison of the accompanying drawing of a blue- 

 bottle's wing (Fig. 56) with those of the larger and 

 smaller house flies given on p. 174 will further show 

 what sort of differences may be expected in this respect. 

 The present plan is very much like that of the house fly 

 proper, and the chief difference is in the prsebrachial 

 nervure (the third 011 the disc of the wing towards the 



FIG. 56. Wing of Bluebottle (Calliphora). 



tip). In the present species it will be found first to bend 

 at right angles towards the nervure above it, and then 

 to slope towards the margin, while the little cross 

 nervure (discal transverse) which joins it to the next 

 below, meets it very much nearer its upward bend than 

 in Musca domestica. The front edge of the wing is 

 bounded by the strongest of all the nervures, the costal, 

 which is furnished, towards the base, with a row of short 

 bristles. To the naked eye the wing appears to con- 

 sist only of membrane, and to have no clothing of any 

 kind ; but microscopic examination shows a multitude of 



