Automatic transmission plug? suppose to be exposed?

[killertofu]

I looked under my car this weekend and noticed that there is a hole in the transmission case. Is there supose to be a plug there? I attached a picture of what I'm talking about. There is a red circle around the hole. I tried doing a search but couldnt find anything.

I would really appriciate it if someone can tell me if its suppose to be exposed or not.

Thanks