I would assume that you mean that is missing from the Layers, Channels, Path box.  If so, then when you see the Path option displayed, you will see an X to the right of the box that will close the tab and to the left of that a triangle pointing to the left.  If you click on the triangle pointing left, you will get an option to add a tab, and when you choose that, you will be able to add the layers option back in.

I hope that this is what you were looking for.