How does a spider stretch its legs? That question is an old zoologist baffler. Spiders have no leg-stretching muscles, yet they have an unquestioned ability to unflex all eight pedal extremities. A Caltech biologist, after long study, has finally solved the riddle: the answer is blood pressure.
With delicate and precise instruments, Biologist C. H. Ellis studied many kinds of spiders, including tarantulas and the poisonous black widow. Microscopic examination of their leg membranes, joints, tissues and nerves got him nowhere. But he noticed that even a dead spider leg would stretch if...
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