Importing Newer Emails stored on Hard Drive Into Apple Mail

Greetings Friends,

Following replacement of a failed internal hard drive on a MacBook Pro 17" running OS X Lion 10.7.5, a re-install of the Lion OS, and use of Migration Assistant to restore data from a CCC backup, there's a small issue with Apple Mail (POP mail) that needs to be resolved. Before we had determined that the internal hard drive had failed, there was a period where I downloaded two or three weeks of emails. I then exported the entire Mail Folder from the User Account Library to an external hard drive. Having restored all my old email via Migration Assistant, I need to import the two or three weeks worth of emails from the Mail Folder that was on that external hard drive. I've actually now moved that folder to my desktop, so I need to essentially import the newer emails from the Mail Folder on my desktop, into the identical email accounts in Apple Mail, without deleting any of the older messages. I guess I'm trying to merge the folders… Any suggestions?