Humpty Dumpty?

I just had a startling realisation in Art Class right now. A kid in my class was singing Humpty Dumpty. You know the tune. "Humpty Dumpty sat on a wall. Humpty Dumpty had a great fall. All the king's horses and all the king's men couldn't put Humpty back together again" that one. On the story books there's a cute little egg on the front sitting on a wall. I've just had a haunting realization.

Nowhere in the nursery rhyme does it say Humpty Dumpty is an egg...