1885-86.] Edinburgh Naturalists' Field Club. 331 



as far back as 1869 Mr Suffolk ascribed the consumption of the 

 food to the rasping action of the pseudo-trachea^, which he figured 

 and described in the ' Monthly Microscopical Journal ' of that year. 

 His views, however, on that point, have not been generally enter- 

 tained ; and, with the exception of Mr Hunt and Mr Saville Kent, 

 nearly all other writers on the subject imply that the food is con- 

 sumed by means of the solvent action of the saliva alone. 



Feeling interested in this question, for two or three years past 

 I have fed these flies under the microscope, and in the most favour- 

 able position for observation ; and I was finally forced to the 

 conclusion that the food was consumed by the joint action of the 

 pseudo-tracheee and teeth, the saliva merely acting as the vehicle 

 which received the scraped-off particles. The food was thence 

 sucked back into the mouth, before entering which it was probably 

 subjected to the further action of the teeth. I regret that I am 

 unable to-night to show you the living proboscis at work, as I am 

 certain it would have interested you more than a mere description. 

 The usual plan, however, has been to put the fly into the live-box 

 along with a piece of sugar or meat, and to watch its movements 

 under the microscope ; bi;t in this way, the back of the fly being 

 towards the observer, very little information could be gained. 

 Another plan was to put the fly in the live-box, with a spot of 

 syrup on the cover ; but in this way, again, the fly was com^jelled 

 to suck, and the real function of the pseudo-trachefB never came 

 into play. The plan I adopted was to place a drop of rice-paste 

 on the centre of a glass slip ; then, taking the fly by the legs, its 

 back was set on the drop, which extended to the margin of the 

 wings and held it fast, when, after kicking for a few minutes, it 

 became quiet, and reconciled to its temporary bondage. The fly 

 was next put on the stage of the microscope, and with the aid of 

 the bull's-eye condenser, a strong beam of light was thrown upon 

 the head. The fly now being on its back, with the j^roboscis 

 directly under the objective, the whole process of eating could be 

 distinctly seen, and in this position the fly would continue to eat 

 till one was tired of observing. Two motions could be noticed — 

 a rasping or filing and what I would call a biting or snapping 

 motion, just as if the fly was trying to obtain a firmer hold of the 

 sugar ; and some light is thrown on these movements by an 

 examination of the slide I have prepared. In the first place, we 

 find the lobes are channeled with numerous false trachere, usually 

 twenty-nine or thirty on each lobe, although this number is not 

 always constant. These tracheaa may be described as open tubes, 

 like a piece of india-rubber tubing slit lengthwise, and kept open 

 by semicircles or half-hoops, each semicircle terminating at one 

 end in the form of a fork and at the other in a blunt point, so that 

 throughout the greater length of the tube we have alternately a fork 



