Memory Alpha summary
Remember that Next Generation episode, "Liaisons," where alien ambassadors take a variety of ways to explore how the crew reacts (Troi gets the best one, because they spend the whole time eating chocolate)? Well, "Bem" is kind of exactly that episode, except with a colony alien.
Colony alien? Imagine the Trill (most memorably embodied by Jadzia and Ezri Dax), who have humanoid hosts and slug-like symbionts, but with a far more incomprehensible setup. This time the body breaks down into independent component parts, such as the torso being able to separate, and the lower body producing an entirely new set of arms to compensate.
It's kind of completely insane, but the episode pulls it off. The more time you spend time with Bem, the more you like him, regardless of how exasperated he makes Kirk. (Actually, Kirk is exasperated throughout most of the series.)
Speaking of Kirk, "Bem" establishes his middle name as being Tiberius. That's another historic element that should settle the matter of whether or not this series should be considered canon. I mean, right?
But then, I guess the counterargument will always be, but weirdo concepts like Bem exist too...
four quarter analysis