6 INTRODUCTION 



The house-fly, together with the blow-fly and the blood- 

 sucking flies Stomoxys and Glossina, belongs to the family 

 Muscidae, which is characterised by having the terminal joint 

 of the antenna, the arista, always combed or plumed, and by the 

 absence of large bristles or macrochaetae on the abdomen. The 

 Muscidae, together with the Anthomyidae and Tachinidae, con- 

 stitute the group Muscidae calypteratae, which are characterised 

 by the possession of squamae, small lobes at the bases of the 

 wings which cover the halters. In the acalyptrate muscids the 

 squamae are absent or rudimentary. These two groups belong 

 to the sub-order Gyclorrhapha, one of the two primary divisions 

 of the Diptera. The Gyclorrhapha have coarctate pupae, the 

 pupal case being formed by the hardening of the last larval 

 skin, and the flies escaping through a circular orifice formed by 

 the fly pushing off the end of the pupa by means of an inflated 

 sac-like organ — the ptilinum or frontal sac — which is after- 

 wards withchawn into the head, its presence being marked by 

 a fi-ontal crescentic opening — the lunule. The other sub-order, 

 the Orthorrhapha, have obtected pupae. 



The most complete specific description of Musca doniestica 

 has been given by Schiner (1864), of which the following is 

 a free translation : 



" Frons of male occupying a fourth part of the breadth of the 

 head. Frontal stripe of female narrow in front, so broad behind 

 that it entire!}- fills up the width of the frons. The dorsal 

 region of the thorax dusty gTey in colour, with four equally 

 broad longitudinal stripes. Scutellum gi'ey, with black sides. 

 The light regions of the abdomen yellowish, transparent, the 

 darkest parts at least at the base of the ventral side yellow. 

 The last segment and a dorsal line blackish brown. Seen from 

 behind and against the light the whole abdomen shimmering 

 yellow, and only on each side of the dorsal line on each segment 

 a dull transverse band. The lower part of the face silky yellow, 

 shot with blackish brown. Median stripe velvety black. Antennae 

 broAvn. Palpi black. Legs blackish brown. Wings tinged with 

 pale grey, with yellowish base. The female has a broad velvety 

 black, often reddishly shimmering frontal stripe, which is not 

 broader at the anterior end than the bases of the antennae, but 



