Eymorgs were humanoid aliens lived on the sixth planet in the Sigma Draconis system. The term Eymorgs specifically referred to the female gender, whereas the male of the species were just called Morgs. As such, use of the term "female Eymorg" is a bit of a redundancy.
More than 8,000 years ago, the sixth planet in the system was struck by a massive glacial age, which wiped out most of the advanced culture that existed there. Those that survived created an underground city for the women to survive in, while the males remained on the surface. An advanced computer system, known as the Controller, was left behind to administer to all of the Eymorgs' needs.
By the mid-23rd century, the Morgs had descended into a state of primitive barbarism, while the Eymorgs suffered mental atrophy living below ground. What little intellect they did maintain was enhanced through a mechanism they called the Great Teacher. As the knowledge given by the Great Computer yielded only a temporary effect, the Eymorgs sought to improve upon this by stealing the brain of the Federation Starfleet officer Mister Spock. Needless to say, Mister Spock's comrades aboard the USS Enterprise did not take kindly to this cranial misdemeanor and a landing party journeyed to the planet to retrieve Mister Spock and his brain.