Why are the contents of a message folder there on my iPad but not my iMac?

On my iMac, the list of Mailboxes on the left of my Mail window shows a mailbox with the same name under both the "on my Mac" heading and the "iCloud" heading. but neither Mailbox appears to contain any contents. The Mailbox with the same name is on my iPad and has all the messages that should be there. I want the is data available on both my iMac and my iPad. My iCloud I/D on my iMac is my me.com e-mail address and that on my iPad uses the mac.com e-mail address. I use Mavericks 10.9.4 and IOS 7.1.2