In the fall of 1981 Mork and Mindy were married, and honeymooned on Ork. Shortly thereafter Mork gave birth, by ejecting a small egg from his navel. The egg grew and grew and finally cracked open to reveal their 225 pound son, Mearth (played by Jonathan Winters). At the end of each episode Mork reported back to his leader Orson, on Ork, twisting his ears and signing off, "Na nu, na nu"--good-bye in Orkan.
http://www.classic-tv.com/shows/morkandmindy.asp
Dumb show, but Robin Williams and Jonathan Winters were irresistible and made us all watch.