Of all the episodes of all series, this one holds the closest to Roddenberry's original tenet. According to the book THE MAKING OF STAR TREK, in Roddenberry's writer's guide to his story writers, he states that any alien creature, no matter how hideously ugly, impossible to believe, benign or malicious, MUST hold some semblance of humanity that the TV viewing public can empathize with and/or relate to. Devil In The Dark's HORTA, which resembles nothing more or less than a large blob of cow dung, is a mother protecting her babies, those ball-shaped silicon nodules the miners keep finding throughout the mine passages and destroying, because they have no idea what they are! This is one of my absolute favorite episodes if only for that!