130 B. T. LOWNE ON THE PROBOSCIS OF THE FLY. 



the fly, in the pupa state, this is even more apparent. In the 

 early stages these trachese are only indicated by transverse lines in 

 a flat membrane, the edges of which curl over as the insect ap- 

 jDroaches maturity ; but in the adult fly, if the recent lips be ex- 

 amined, it will be found that the tubes are covered by broad bands 

 of tissue, having a sinuous margin, and refracting light powerfully. 

 By examining the pupa proboscis, these will be seen to be reflected 

 from the margins of the false tracheae, leaving an exceedingly 

 minute fissure along the mesial line, on each side of which, lateral 

 fissures extend at right angles across the tracheal tube, one corres- 

 ponding to each dentation in the trachea itself. These fissures are 

 60 minute, that it requires a quarter-inch objective to show them 

 clearly. They probably serve to allow air to pass to and from the 

 false trachete, but do not allow fluids to pass into them, a fact I 

 have demonstrated by feeding flies with coloured syrup. 



During the life of the fly, the lips of the proboscis are not usually 

 opened to more than two-thirds of their extent ; this is effected by 

 the muscles attached to the thin extremities of the maxillee, which 

 are then drawn at right angles to the remainder of the maxillary lobe, 

 (the combined inner surfaces of the lips, in this position, form an 

 oval sucker, reminding one somewhat of the sucker of Kemora,) com- 

 municating through the fissure between the lips, with a cavity (labial 

 cavity) bounded behind by the triangular opening of the labial tube, 

 and in front by the remaining third of the lips. The false tracheae 

 open directly into this cavity, and are so connected with the labial 

 tube, and through it with the whole air system of the insect. If 

 the lips be examined by the aid of a Leiberkuhn in the living fly, 

 whilst sucking in a live box, which may easily be accomplished by 

 moistening the thin glass with a very small quantity of syrup, and 

 allowing it to dry, it will be seen that the sucker formed by the com- 

 bined lips is closely applied to the glass at its edges. That the fluid 

 previously poured by the insect upon the sugar is drawn into the 

 sucker by the exhaustion of the air through the false tracheal 

 tubes, seems most probable, from their connection with the tracheal 

 system. 



Any one may convince himself that the readiest manner of ex- 

 tracting the sweet fluid from moistened sugar is by drawing air 

 through it ; so we see Nature has provided these insects with a 

 special organ for overcoming capillary attraction, by calling in the 

 aid of atmospheric pressure. I think it is probable that the ceso- 



