## **Core Concept**
The perivitelline space, also known as the perivitelline or subzonal space, is a critical region in the structure of an ovum (egg cell). It is the space between the plasma membrane of the oocyte (zona pellucida) and the outer layer of the zona pellucida. Understanding the contents of this space is essential for knowledge of fertilization and embryology.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the perivitelline space contains the **cortical granules**. Cortical granules are specialized organelles found in the oocytes of many species, including humans. They are involved in the cortical reaction, which is a critical event during fertilization. When a sperm penetrates the zona pellucida and fuses with the oocyte, cortical granules release their contents into the perivitelline space. This release leads to modifications of the zona pellucida, making it impenetrable to additional sperm and thus preventing polyspermy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the contents of the perivitelline space.
- **Option B:** This option is incorrect as it does not specify cortical granules, which are known to be in the perivitelline space.
- **Option D:** This option is incorrect because it inaccurately describes the contents of the perivitelline space.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the cortical reaction and the contents of the perivitelline space play a crucial role in **preventing polyspermy**, a condition where an egg is fertilized by more than one sperm. This is vital for normal development and genetic integrity of the offspring.

## **Correct Answer:** . Cortical granules.