Why a hole in the diff case?

[tobbe]

Maybe a stupid question but this has disturbed me for a long time...When I look at the pics of the BJ4's rear diffcase, it's seems like it have a big hole between the two case halves?? If it is a hole there, why? For what reason? The diff can't hold for long if it comes dirt and sand in there



Please tell me why it looks like that. I'm just a bit curious why it looks like that