on the Mac desktop, they are not actually ON the Mac desktop.
They are actually completely separate volumes that basically have an alias (shortcut) on the desktop.
Looks like your external drives are not shared.
Go to System Preferences > File Sharing and ADD the external drives to the list.
Give suitable permissions to them.
That should do it.
I have an old G4 laptop with two LaCie hard disks attached. I want to share the LaCie disks with my Windows computer that has a local network connection. I have pored over the Mac Help for information on this, but can't find any mention of it. Windows can see the Mac desktop, except for the mounted disk drives. Can this be done?