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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 399 



lower parfc of the face silky yellow, shot with blackish brown. 

 Median stripe velvety black. Antennse brown. 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 becomes 

 so very much broader above that the light dustiness of the 

 sides is entirely obliterated. The abdomen gradually be- 

 coming darker. The shimmering areas on the separate 

 segments generally brownish. All the other parts are the 

 same as in the male." 



The mature insects measure from 6-7 mm. in length and 

 13-15 mm. across the wings. Flies which have been starved 

 during the larval stage or subjected to adverse conditions are 

 generally smaller in size. 



II. METHODS. 



All the details of the anatomy which are about to be 

 described have been studied by means of dissections. The 

 dissections were made on both fresh and preserved material 

 under a Ziess' binocular dissecting microscope with magnifi- 

 cations varying from 25-65 diameters. Serial sections have 

 been made to confirm the dissections and to study the histo- 

 logical details. 



Perfect series of sections of the whole fly were hard to 

 obtain on account of the somewhat brittle nature of the in- 

 ternal chitinous structures. These internal chitinous skeletal 

 elements caused the greatest trouble as they were apt to 

 damage the internal anatomy. Celloidin sections were not a 

 great improvement on those cut in paraffin. The best results 

 were obtained by fixing the flies from 12-24 hours in 

 Henning's solution, which is Nitric acid 16 parts, chromic 

 acid (*5 per cent.) 16 parts, corrosive sublimate saturated in 

 60 per cent, alcohol 24 parts, picric acid saturated in water 

 12 parts, and absolute alcohol 42 parts, washing out with 

 iodine alcohol. This not only fixes, but to a certain extent, 

 though not completely, softens the chitin. They should not 



