I recently realized something. Single panel cartoons are in fact memes. Never mind that they precede the Internet by over a century; they consist of an image and customarily either a caption, headline, or dialogue that modifies the interpretation of the image, usually for humor. The only way they are "cartoons" is the choice of using drawing styles associated with the art form.

I remember that Scott McCloud tripped over this in his book Understanding Comics, but then he pretty much shrugged it off and kept going.

I'm certain I'm late for figuring this out, but I don't recall anyone else saying it before now.