 In the original production order, skin of evil was episode 1.22. The  order was changed. This was because Denise Crosby had asked Gene  Roddenberry if she could remain on the show for symbiosis. She had  gotten a hold of the script, and thought it was interesting, so she  asked if her characters death could be delayed for one more  episode. Gene Roddenberry granted her request, and had the  production orders for the two episodes switched, so there would be  no continuity issues. Also explains why shes waving goodbye at the  end of this episode.