What does this old mark mean?
It is an "Ideographic Full Stop"1
In some Asian languages, notably Chinese and Japanese, a small circle is used instead of a solid dot: "。" [Source]
@KaiserOctavius encouraged me to search a bit more and although most of the links I found searching that quote didn't have the "。", one result did have the "degree sign" °.
On that page, it appears the author was just using these marks as links to the glossary, indeed, clicking the symbol took me to a glossary entry for pathetic.
1. I didn't get this as a linguist, I got this is a programmer! I found a "Character to ASCII converter" and used that to find out the hexadecimal ID of the character, then I used another online tool to find out the character's name, then googled that name. Rinse and repeat for other unknown characters
If I might clarify James Webster's point, I think the lesson here is that the questioner's source (directly or indirectly) is a modern electronic version which included hyperlinks to editorial notes, and he or she is mistakenly interpreting the hyperlinks as 'old marks' in the original.