pre-thoughts on ampersands

A friend and I were talking about ampersands earlier today -- these things: "&" -- and we were trying to figure out what makes them ... I don't know, tick? Because they look so different in so many places. Sometimes they look like a cursive G, or a treble clef, sometimes they look like a backwards E, and sometimes then there's a line through it -- what makes them recognizable? What makes them functional as a symbol?

This post isn't an answer, it's just a public record that I've been wondering. I doubt I'm going to actively research it, but having written this blog post if the information ever floats past me I'll almost definitely retain it; in which case, I will report back.