Schizophora is a section of true flies containing 78 families, which are collectively referred to as muscoids, even though - technically - the term "muscoid" should be limited to flies in the superfamily Muscoidea; this is an example of informal, historical usage persisting in the vernacular. The section is divided into two subsections, the Acalyptratae and Calyptratae, which are commonly referred to as acalyptrate muscoids and calyptrate muscoids, respectively.
The defining feature of the Schizophora is the presence of a special structure that is used to help the emerging adult fly break free of the puparium; this structure is an inflatable membranous sac called the ptilinum that protrudes from the face, above the antennae. The inflation of the ptilinum (using fluid hemolymph rather than air) creates pressure along the line of weakness in the puparium, which then bursts open along the seam to allow the adult to escape. Once the adult emerges, the fluid is withdrawn, the ptilinum collapses, and the membrane retracts entirely back inside the head. The large, inverted "U"-shaped suture in the face through which it came, however, is still quite visible, and it is this ptilinal suture or frontal suture from which the name "Schizophora" ("split-bearers") is derived. The term was first used by Eduard Becher .
Source: Wikispecies, Wikipedia: All text is available under the terms of the GNU Free Documentation License