It is followed in some specialized Heteropoda and in the Euthyneura by a torsion in the opposite direction, or detorsion, which brings the anus farther back and untwists the visceral commissure (see Euthyneura, below).
This figure shows how the wing twists and untwists when in action, and how it forms a true screw.
These show the screw-like configuration of the wing, and also how the wing twists and untwists during its action.
It, moreover, twists and untwists during its action and describes figure-of-8 and waved tracks in space, precisely as the natural wing does.
Which twists and untwists during x or screw.
How would you define untwists? Add your definition here.