[SOLVED] How do I reinstate default Network & Volume control icons on the Panel?

[m654321]

After booting up today, I noticed that on the Panel, that runs horizontally along the bottom of the laptop display, the usual icons for Network and Volume Control were missing.  These icons come by default when LL is installed, and are located on the right-hand end of the Panel bar.  The Network one is particularly useful as it allows me to switch network for the Wi-Fi connection  and also shows me the internet connection speed.  The Volume icon is also useful as it allows me coarse control for Clementine or other media players.

I don't know why they are missing - maybe I inadvertently clicked on something?
How do I reinstate them?

Many thanks, as ever,  for your kind help...

Regards
Mike