1873.] 147 [Packard. 



The prothoracic spiracle, with its black, corneous tip, is much the 

 same in all the specimens. 



Having had more alcoholic specimens of the pupa of Stomoxys 

 than of Musca, we have not been able to trace these stages in the 

 latter genus, but doubt not that similar ones occur in all the Muscidse. 



The imago. On leaving its puparium the fly runs around, with its 

 wings soft, small and baggy, much as in the pupa. They reach a 

 little beyond the middle of the abdomen, and are still pressed to the 

 side of the body. It is pale, as in the puparium, and the colors are 

 not set. The membranous portion of the front is constantly distend- 

 ing as the fly walks rapidly about. When this part is contracted it 

 forms a dull livid area, soft and fleshy, free from hairs. This portion 

 suddenly distends into a bladder-like expansion, trapezoidal in out- 

 line, equal in bulk to the rest of the head, and pushing the antennae 

 down beneath out of sight. This thin membrane is evidently dis- 

 tended with air, and its connection with the trachea?, and the mech- 

 anism of its movements, would form a most interesting subject of 

 inquiry. This part has been described by Mr. T. B. Lowne, in his 

 work on the " Anatomy of the Blow Fly," and he is evidently cor- 

 rect in regarding it as an organ for pushing away the end of the 

 puparium when the pupa slips out of its case. 



The common House Fly, though so abundant, is difficult to distin- 

 guish from the allied species. The generic characters may be foand 

 in the mouth-parts, already described by authors. In the venation of 

 the wing it differs decidedly from Sarcophaga, in the end of the me- 

 dian vein being bent nearly at right angles, and in being regularly 

 but slightly incurved, while in Sarcophaga, it is bent at a much lower 

 angle, being much more oblique. From the genus Lucilia, which it 

 much nearer approaches structurally, it differs in this vein being still 

 bent at a greater angle, and in having the bent extremity more curved. 

 In Stomoxys this vein is but slightly bent, thus widely differing, be- 

 sides in its remarkably long horny beak, from Musca, with its short 

 fleshy bilobed tongue. 



The body of M. domestica is black ; the head has a longitudin. 1 

 reddish oval smooth area on the vertex, with the orbits and adjacent 

 region golden (or silvery in some lights) ; the hairs are black, and 

 the antennas and plume are black. The thorax is black, tinged with 

 golden gray on the sides, with three dorsal gray longitudinal bands, 

 the middle one most distinct, the two lateral ones partially inter- 

 rupted in the middle and continued on to the scutellum; there is a 



