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above I should think the vacuum theory the most tenable. I 

 believe the hairs are curved at their extremities, as one frequently 

 finds in the case with all slender filaments ; but I cannot think 

 those curved hairs would be sutificiently stiff to act as hooks. 

 Some time since 1 examined the parasite of the House-fly alive, 

 and think I sent a sketch showing the vacuum producing arrange- 

 ments in their feet. In their case the movement of attachment 

 and detachment was instantaneous, and I could not discover any 

 sign of a gummy matter on the glass. If a gummy substance were 

 used to assist the walking of a fly, we might hope to find foot- 

 prints on polished glass. I have, however, never heard of this 

 discovery. T. R. Barrett. 



I have examined the slide, "Foot of Breeze Fly," with i/i6th 

 immersion o.g., and am satisfied that some, but not all, of the 

 hairs are curved towards the extremity, but whether sufficiently to 

 be of service in grasping irregularities, I am not able to give an 

 opinion. I'he tubular character of the individual hairs can 

 clearly be made out. Annie Pennington. 



I think these hairs are well seen with a low-angled ^-in. o.g., 

 especially on a dark ground ; there are no " hooks," the hairs are 

 slightly curved, but apparently only sufficient to make the ends 

 perpendicular to the surface walked on ; the ends appear as blunt 

 as if cut off with a sharp instrument. This class of object is 

 seen better when prepared in glycerine. Balsam renders them 

 too indistinct. R. Smith. 



The why and wherefore a fly clings to polished surfaces, such 

 as glass, is a subject very much unsettled, and yet high authorities 

 seem to agree somewhat. Dr. Carpenter says : — " The foot is 

 furnished with a pair of membranous expansions termed pulvilli. 

 These are beset with numerous hairs, each of which has a minute 

 disc at its extremity. This structure is evidently connected with 

 the power which these insects have of walking over smooth sur- 

 faces in opposition to force of gravity, yet there is considerable 

 uncertainty as to the precise mode in which it ministers to this 

 faculty. Some believe that the discs act as suckers, the insect 

 being held up by the pressure of air against their upper surface 

 when a vacuum is formed beneath ; whilst others maintain that 



