244 Transactions of the 



trachea would probably occupy when in preparation for the exercise 

 of its suctorial functions ; and I do not think I strain probabihties 

 in believing that these membranous expansions attached to the 

 chitinous crescents, arranged in a double row on each proboscis or 

 pseudo-trachea, may be taken to be suckers, either for the adhesion 

 of the fleshy tongue, or for the imbibition of fluids, or perhaps for 

 both purposes. The view particularly favouring this is well seen 

 in Fig, 2, where a little of the interior of the tube is visible. I 

 take it that by this arrangement, shown in the drawing, each 

 sucker, opening into the tube, and supported by the chitinous 

 crescent, can be applied to any flattish surface, and can be made 

 to serve, as I said before, either for imbibition, or simply for the 

 purpose of adhesion. 



I am disposed to think that, looking at these figures, which I 

 have drawn most carefully and conscientiously from preparations, 

 the majority of which I still possess, that the chitinous rings form a 

 very important part of the mechanism of the suctorial parts of the 

 fly, as these, in the quiescent state of the tongue, by their elasticity, 

 keep the fissure open, and at the same time keep what I take to be 

 the suckers ready for instant action. These rings, or, as they should 

 be called, arches, are imbedded in a fleshy material, which I fancy 

 to be principally muscular, which, brought into action, would bend 

 the chitinous arches till their extremities would be in apposition, 

 when the longitudinal fissure would thus be closed, and only a 

 series of openings left from the suckers into the pseudo-trachea 

 through the crescent portions. 



Assuming the elasticity of these chitinous rings as playing a 

 part, then the operation of sucking with the tongue applied to any 

 surface might be thus described. 



The fleshy lobes of the tongue being forced into close contact 

 with the said surface, the same muscular pressure round the chitin- 

 ous rings would diminish the calibre of the pseudo-trachea, make it 

 into a tube by closing the longitudinal fissure, and bring the bell- 

 like mouths of what I regard as principally the organs of adhesion 

 into the position and semblance of so many cupping glasses. So 

 arranged, I take it that the relaxation of muscular efibrt would, by 

 allowing of the resiliency of the chitinous rings, cause a vacuum 

 in the tube, and set up a pumping process ; and by alternate mus- 

 cular action, fluid in the pseudo-tracheae would be forced into the 

 oesophagus, while the same pressure would make the adhesion more 

 perfect. 



This may appear fanciful. I could hardly claim it as meeting 

 all possible conditions ; but so far as it goes, it seems to me fair to 

 assume it as being in accordance with well-known physical laws, 

 and the appendages I have figured and attempted to describe 

 appearing to have an analogy with the sucking or rather sucker- 



