gaping hole

Hi everybody. Just bought a defender a couple of weeks ago. I don't know much about fixing cars, so I thought this would be a good place to learn. I was looking to change the engine and gearbox oil when I found this gaping hole in the bottom between the engine sump and the gearbox. It seems to be the cause of the oil patch on my driveway. Can anyone identify this component and tell me how to plug the hole.
Many thanks for your help.

Looks like the bellhousing drain, you put a plug in it when wading in deepwater and its supposed to look like your photo, if you have oil leaking from this point the chances are the rear crank oil seal has failed. Oh and hello by the way.

as above but check its not clutch fluid first

Thanks for your help guys. It looks very much like engine oil to me. Possibly due to me overfilling the oil one windy night after driving it for 12 long hours.