Implantation is the process of

The correct option is attachment of blastocyst to the uterine wall.

Implantation is a crucial stage in early embryonic development. Let us break down the process step-by-step to understand why this option is correct:
1. Fertilization: The process begins when a sperm fertilizes an egg in the fallopian tube to form a single-celled zygote.
2. Cleavage and Blastocyst Formation: As the zygote travels toward the uterus, it undergoes rapid cell divisions. It transitions from a solid ball of cells (morula) into a hollow, fluid-filled structure composed of an inner cell mass and an outer layer. This structure is called a blastocyst.
3. Implantation: Upon reaching the uterus (usually 5 to 7 days after fertilization), the blastocyst adheres and embeds itself into the endometrium, which is the nutrient-rich inner lining of the uterine wall. This process of attachment and embedding is known as implantation, and it allows the developing embryo to receive oxygen and nutrients from the mother's blood supply to grow.

Let us look at why the other choices are incorrect:
- Egg movement: This refers to the transport of the egg from the ovary through the fallopian tube, which happens before fertilization.
- Egg fertilization: This is the initial fusion of the sperm and egg cells, which occurs in the fallopian tube long before implantation.
- Degeneration of egg: This happens when fertilization fails to occur, leading to the breakdown of the egg and its shedding during menstruation.