Wrapping the armadillo's penis

摘要

A multitude of soft-bodied organisms (such as worms) and parts of organisms (such as the tube feet of echinoderms, the trunks of elephants, and even our own tongues) are biological hydrostats. They lack solid skeletons, yet hold their shape because ofthe internal fluid pressure, which is resisted by tension in the sheath that surrounds the fluid space. These enwrapping sheaths are reinforced with fibres that classically spiral up and down the long axis of the structure, forming a crossed helical array.