Here's a sircular structure with a hole in the middle. Is actually a transverse section of the appendix vermiformis. The hole is the lumen and all the stuff around it can easily be divided 3 distinct layers:
- tunica mucosa (mucosa)
- tela submucosa (submocosa)
- tunica muscularis (the muscular layer)
One of the most characteristic properties of the appendix is the presence of lymph follicles in the mucosa and submucosa as seen in this image. These lymph follicles contain germinal centers like the ones in the small intestine called Peyers patches.