Color enhanced scanning electron micrograph (SEM) of the entrance into one of the oviducts from the uterus. The oviduct, or fallopian tube, is a tube that passes eggs from an ovary to the uterus. Oval shaped epithelial cells are also visible. These cells make up the endometrium, the inner wall of the uterus. During the menstrual cycle, the endometrium builds up in readiness for a fertilized egg. If the woman does not become pregnant, this tissue layer is shed at the end of the cycle.