7 8 NORTH AMERICAN DIPTHRA. 



and they are often difficult of discernment. I am not 

 disposed to place a large degree of reliance upon char- 

 acters so inconstant. 



It will be observed that, as in the former edition, I fol- 

 low Schiner in arranging the Myodaria in a reverse order 

 from that usually given in systematic works and cata- 

 logues. In the holoptic eyes, enlarged squamae, greater 

 development of the bristles, entire absence of apical 

 arista, and larger size, the Calypterae demonstrate their 

 high rank among the Cyclorrhapha ; and they of course 

 could not have been the ancestral type from which the 

 Acalypterae arose. The Acalypterae are for the most 

 part a divergent branch with certain decadent special- 

 izations like those of the oligoneurous Nemocera. The 

 relationships between the Tanypezidae or Micropezidae 

 and certain forms which by common consent are placed 

 among the Conopidae, are beyond all dispute; indeed in 

 my opinion the Conopidae should be included among the 

 Myodaria, as they w 7 ere by Desvoidy. 



PUPIPARA. 



The singular group of flies known as the Pupipara or 

 Eproboscidea is composed wholly of ectoparasites infest- 

 ing mammals, birds and other insects, living among the 

 hair or feathers of their hosts and subsisting upon their 

 juices. This parasitic habit has induced many remark- 

 able modifications of structure, as would be supposed. 

 The compound eyes are never large, and, in those flies 

 living upon the crepuscular or nocturnal bats, they have 

 become reduced to the merest vestiges. So, also, the 

 ocelli are in general degenerate and often wanting. The 

 antennae are short, the joints often apparently reduced 

 in number, and they are often bristly. The mouth-parts, 

 while still retaining all the constituent parts of most 

 other cliptera, have become much abbreviated, and are not 



