MUSCIDAE ACALYPTRATAE 



503 



wants elucidation. Whether the Syrphidae, or some of them, 

 possess a ptilinum that helps them to emerge from the pupa is 

 more than doubtful, though its existence has been affirmed by 

 several authors of good repute. 1 



Series 4. Cyclorrhapha Schizophora 



Fam. 33. Muscidae acalyptratae. This group of flies has 

 been the least studied of all the Diptera ; it is generally treated 

 as composed of twenty or thirty different families distinguished 



FIG. 240. Diopsis 

 apicalis. Natal. 

 A, The fly ; B, ex- 

 tremity of cephalic 

 protuberance, more 

 magnified. a, 

 The eye ; b, the 

 antenna ; c, middle 

 of head, frout 

 view ; c, ocelli. 



by very slight characters. It is, however, generally admitted by 

 systematists that these assemblages have not the value of the 

 families of the other divisions of Diptera, and some even go so 

 far as to say that they are altogether only equivalent to a single 

 family. We do not therefore think it necessary to define each 

 one seriatim ; we shall merely mention their names, and allude 

 to certain points of interest connected with them. Taken collec- 

 tively they may be denned as very small flies, with three-jointed 

 antennae (frequently looking as if only two -jointed), bearing a 

 bristle that is not terminally placed ; frequently either destitute of 

 squamae or having these imperfectly developed so as not to cover the 

 halteres ; and possessing a comparatively simple system of nervura- 

 tion, the chief nervures being nearly straight, so that consequently 

 few cells are formed. These characters will distinguish the group 

 1 See on this difficult subject, Becker, Wien. ent. Zeit. i. 1882, p. 49. 



