Partial Reprint of MERCURY WORM article in the Florida Wildlife Magazine. Taken from product literature, not dated:

Such is the Mercury Worm, a ¼ ounce clean and hollow tenite butyrate plastic lure, housing a globule of restless, flashing mercury suggestive of an unhappily imprisoned worm. The new lure is the clever invention of one Ken Clapp. In developing the Mercury Worm, Clapp experimented over a twelve-year period and made and tested more than 150 different models before convinced that he had the very best possible design and action. The lure is now manufactured by Mercury Worm Lure Co. owned by H.H. McJunkin Sr. of Dallas, Texas.

The lure, which casts like a bullet, features 5 body colors, ... with one treble hook gang in the latter section. When cast and retrieved the blob of imprisoned mercury humps itself around inside the clear section like something alive inside a bubble, and the constantly shifting weight of the mercury causes the lure to alternately wiggle, dive and dart on the retrieve.