852 ^^V INTRODUCTION TO ENTOMOLOGY 



of these live in colonies of aphids, and do much good by destroying 

 these pests. 



This family is a very large one; more than 300 species represent- 

 ing about 60 genera have been described from America north of 

 Mexico. Williston ('86) published an extended monograph of our 

 species. 



SERIES II— SCHIZOPHORA* 



Cydorrhapha with a frontal suture 



This series of families includes all of the Cydorrhapha except the 

 four preceding families in which the frontal suture is wanting. In 

 this series, the Schizophora, there is a frontal suture through which 

 the ptilinum is extruded in order to force off the head end of the pu- 

 pariimi when the adult is ready to emerge. 



This series is divided into two quite distinct sections, the Myodaria 

 and the Pupipara. 



SECTION I— MYODARIA 



The Muscids 



This section of the order Diptera is a very large group, including 

 many families and probably more than half of all the living species 

 of this order. As many of the species are very common, it usually 

 happens that a large portion of the flies in a collection belong to the 

 families included in this section. 



Excepting the first family, the Conopidas, the families included 

 in the Myodaria differ from all of the preceding families in that vein 

 Cu2 coalesces with vein 2d A to such an extent that it appears like a 

 cross-vein or is curved back towards the base of the wing; and they 

 differ from the following families, the Pupipara, in having the ab- 

 domen distinctly segmented and the two legs of each thoracic seg- 

 ment not widely separated. 



The antennae are three-jointed; the third segment bears an arista 

 which is almost always dorsal in position. The radial sector is not 

 more than two-branched ; cells Mi and M3 are wanting ; and the two 

 branches of cubitus coalesce with the adjacent veins (Vein Cui with 

 M3 and Cu2 with 2d A) for nearly their entire length, except in the 

 Conopidse. 



The families included in this section are grouped in two subsec- 

 tions, the Acalyptratas and the Calyptratae. 



*Schiz6phora: schizo (<^x'f«), a cleft; phoros {(pop6s), bearing. 



