48 OX THE ANATOMY OF THE FLY. 



sect is enabled to filter the fluid from the solid portion of the 

 substances on which it feeds. The lobes are, however, capable of 

 further separation, exposing the triangular opening which is sur- 

 rounded by from fifty to sixty bidentate rods or teeth, which are 

 usually concealed between the posterior portions of the lobes but 

 are used, when exposed, for grinding hard substances, such as 

 sugar, so assisting the salivary secretion to dissolve them- 4 . Fluids 

 are often drawn directly into the mouth, either by the fissure 

 between the lobes when it is partially closed, or even when it is 

 fully opened to expose the teeth, but they more usually pass 

 through the false trachere. This is best demonstrated by giving 

 the fly a little blood and afterwards examining the proboscis, 

 when all these channels will be found filled with it. 



The parts forming the anterior triangular opening of the mouth are 

 represented in Plate II, Figs. 5 and 5a ; they are a dark solid mass of 

 chitine and two lateral plates, which probably represent the anterior 

 labial plate and the basal portion of its lateral appendages ; they bear the 

 lobes and bideutate rods or teeth, already mentioned, 



The false tracheas, (Plate IV, Figs. 2 and 3,) are channels on the anterior 

 surface of the lobes, kept open by semi-rings, which are developed from 

 cells of the protoderm. These rings are bifurcated at one extremity, and 

 the bifurcated extremity is alternate in the several ringsf. The channels 

 become gradually smaller towards the edge of the disc and terminate in 

 closed extremities. Their number is variable and not always the same of 

 the two sides of the proboscis ; there are generally twenty-nine or thirty 

 on each side. They usually open on the inner edge of the lobes in the fol- 

 lowing order. The five anterior channels unite and form a large trunk, 

 which runs along the upper border of each lobe and opens close to the upper 

 margin of the triangular opening ; the next seven or eight open separately, 

 each externally to a set of teeth, and the remainder run into a pair of 

 parallel channels in the middle of the disc below the opening of the 

 mouth, which open at the lower part of the triangular opening. Between 

 the margin of the triangular opening and the orifices of the false tracheal 

 channels, a number of curved chitinous pillars are found radiating from the 

 gides of the triangular opening to these orifices ; they arc distinctly seen 

 to represent the semi-rings of 4he channels themselves flattened out. 



*f Some very interesting information on this subject with good figures of 

 the details of the false trachere, is given by Mr. W. T. Suffolk, in a paper 

 read before the Eoyal Micros. Soc. Ap, 14. 1869. 



* Described by Mr. Hunt, Microscopical Quarterly Journal, 1856, p. 238. 



