I've been watching the Season 1 disc and Marsha Warfield took her place not too many episodes into the first season - what happened? I love Marsha Warfield and think she made a great addition, but wish they hadn't booted Anne Francis.
shareI've never been able to find any solid info on it, but as far as I can make out, Anne Francis decided to move on as the series just found its feet and settled down.
It's actually quite common for some secondary characters introduced in the Pilot to be either dropped from the series, or to go within the first few episodes. Just one of those TV things, I guess.