Mr. Brackwarr 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 pre: 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 domestica, 
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. 
Flies which are unable to maintain an inverted position on 
3n2 highly 
