**Core Concept**
The vaginal wall is a complex structure that develops from multiple embryonic layers. During fetal development, the Müllerian ducts, which give rise to the female reproductive system, interact with the urogenital sinus, a structure derived from the endoderm. This interaction leads to the formation of the vaginal wall, which is composed of both endodermal and mesodermal tissues.

**Why the Correct Answer is Right**
The correct answer is C. Endoderm and mesoderm. The vaginal wall is formed from the fusion of the urogenital sinus, which is an endodermal structure, and the Müllerian ducts, which are mesodermal in origin. This interaction between the endodermal and mesodermal tissues results in the formation of a unique tissue composition. The endodermal component of the vaginal wall is responsible for its lining and mucosal functions, while the mesodermal component provides structural support.

**Why Each Wrong Option is Incorrect**
**Option A:** The vaginal wall is not derived solely from the endoderm. While the endoderm contributes to the formation of the vaginal wall, it is not the sole contributor.
**Option B:** The mesoderm is not the only layer involved in the formation of the vaginal wall. The mesoderm contributes to the structural support, but it is not the primary layer responsible for the formation of the vaginal wall.
**Option D:** The ectoderm is not involved in the formation of the vaginal wall. The ectoderm gives rise to the skin and central nervous system, but it is not involved in the development of the female reproductive system.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the vaginal wall is a complex structure that develops from multiple embryonic layers. Understanding the embryological origins of the vaginal wall can help identify potential anomalies and abnormalities that may arise during development.

**✓ Correct Answer: C. Endoderm and mesoderm**