SUBPUNCTING. Cameron Hunt McNabb had an article in Slate giving the history of ellipsis periods. McNabb traces them to scribes copying medieval manuscripts (and for whom erasing was difficult): “In medieval manuscripts, we find a mark—sometimes called subpuncting or underdotting—that is used to indicate the omission of a word or phrase, usually when that word or phrase has been copied erroneously.” The mark is a series of dots placed under the words which should be omitted.
Subpuncting in manuscripts fades away in the early part of the 16th century and the ellipsis increases in printed books toward the end of the 16th century. McNabb acknowledges that this timing could be coincidental, but suggests that the printers borrowed the dots to show omissions from the subpunct marks which had been used in manuscripts.