One of the works of the French poet Jean de La Fontaine is a collection of stories that's usually known as Contes et nouvelles en vers. It seems to me that this title implies that there was a difference between the genres called "conte" and "nouvelle". Indeed, if you read the book, you can see how the author explicitly called some of the stories "conte", while some others are called "nouvelle", but I don't understand why La Fontaine decided to make such difference.
Can someone explain what was such difference? Has it to do with the length of story?