A Fly Walk On The Ceiling
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Some scientists believe that the discs act as suckers, and that when a fly walks on the ceiling a vacuum is formed between the disc and the ceiling, holding the fly up there by the pressure of the air. Against this theory, however, is the fact that when the air is drawn out of a vessel in which the fly is walking upside down, the insect does not fall off.
Other scientists who have carefully studied the fly believe that it is able to hold on by means of a sticky substance coming from the under side of the foot. Each hair would seem to be a tiny tube for conveying this liquid from the little pouch in which it is produced, pouring it out as required. The fly performs the feat and seems to be defying gravity.
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