Mr. Blackwall on the Pulvilli of Insects. 489 



minated suckers, with which the terminal joint of the tarsi of 

 flies is provided, that it cannot possibly be brought into contact 

 with the objects on which those insects move, by any muscular 

 force they are capable of exerting : the production of a vacuum 

 between each membrane and the plane of position is therefore 

 clearly impracticable, unless the numerous hairs on the under- 

 side of these organs individually perform the office of suckers, 

 and there does not appear to be anything in their mechanism 

 which in the slightest degree countenances such a hypothesis. 

 When highly magnified, their extremities, it is true, are seen to 

 be somewhat enlarged ; but, whether they be viewed in action 

 or in repose, they never assume a figure at all adapted to the 

 formation of a vacuum. 



Satisfied that this difficult problem must admit of a solution 

 more consistent with the various phenomena it comprehends 

 than the popular one here controverted, I determined to insti- 

 tute an experimental investigation of it. Accordingly, having 

 procured living specimens of the House-fly, Musca domestical 

 and of the large Flesh-fly, Musca vomitoria, I inclosed them in 

 clean jars and phials of transparent glass, the interior surface of 

 which they traversed in every direction with the greatest facility, 

 walking upon it even with their backs downward, while they 

 remained in full vigour ; but when enfeebled by exposure to 

 cold, or when fatigued by over exertion, the identical individuals 

 ascended the sides of the same jars and phials with considerable 

 difficulty, falling from them in numerous instances, and they 

 were entirely incapacitated for adhering to them in an inverted 

 position ; yet when their physical energy was restored by repose, 

 or an increase of temperature, they again repeated their most 

 extraordinary feats with all their original promptness and dex- 

 terity, '"-''"i -"'i^'i'. n? ; 

 J ^ Flies which are unable to maintain an inverted position on 



3 R 2 highly 



