on bur oak. They don't form between the leaf layers, but totally on the outside, just tapping into veins, as you can see from the group pulled off and reversed. (Note - the second photo of one cut open also shows a different, much smaller, gall that occurs between veins.) The diameter includes the 'fur'. There is a small white grub inside, but I don't have a dissecting microscope and haven't been able to separate it for a photo - it's about 600 um diameter, about 5x that in length.