Active inrolling of endodermal and mesodermal cells into interior of embryo is

Options

A. Ingression
B. Involution
C. Inversion
D. Epiboly.

Answer

To answer the question regarding the active inrolling of endodermal and mesodermal cells into the interior of the embryo, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Ingression**: This refers to the movement of individual cells from the surface layer into the interior of the embryo during gastrulation.
- **Involution**: This is the process where a sheet of cells rolls inward to form a new layer, specifically referring to the movement of endodermal and mesodermal cells into the embryo.
- **Inversion**: This term typically relates to chromosomal rearrangement, not cell movement in embryonic development.
- **Epiboly**: This is the process where a layer of cells expands to cover a larger area, often seen in ectodermal cells.

2. **Identifying the Correct Process**:
- Since the question specifically asks about the active inrolling of endodermal and mesodermal cells, we need to focus on the options that involve such movements.
- **Involution** is the process that describes the rolling inward of these cells into the embryo.

3. **Conclusion**:
- Based on the definitions and processes discussed, the correct answer to the question is **involution**.

### Final Answer:
The active inrolling of endodermal and mesodermal cells into the interior of the embryo is called **involution** (Option B).

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