**Question:** Primordial Germ cells of ovary are developed from which layer of germ cells?

**Core Concept:** Primordial germ cells (PGCs) are the precursors of oocytes (female gametes) and sperm (male gametes) in both humans and animals. In the context of the ovary, PGCs are derived from the inner cell mass (ICM) of the blastocyst during early embryonic development.

**Why the Correct Answer is Right:** The correct answer, choice "C", refers to the inner cell mass (ICM) of the blastocyst, which is the initial population of cells that will give rise to the embryo proper. These cells differentiate into the three primary germ cell lineages: the primordial germ cells (PGCs), the somatic cells, and the placental cells.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Ectoderm)**: Primordial germ cells develop from the inner cell mass (ICM), not the ectoderm, which gives rise to the neural crest, neurons, and epidermis.
B. **Option B (Mesoderm)**: Primordial germ cells develop from the inner cell mass (ICM), not the mesoderm, which gives rise to blood cells, connective tissue, and skeletal muscle cells.
D. **Option D (Endoderm)**: Primordial germ cells develop from the inner cell mass (ICM), not the endoderm, which gives rise to the gastrointestinal tract, respiratory system, and liver cells.

**Clinical Pearl:** Understanding the differentiation of primordial germ cells from the inner cell mass is crucial for understanding embryonic development and male and female gamete production in humans and animals.

**Correct Answer:** C. Inner Cell Mass (ICM)