Question

Epiboly is the process of
A. Mass migration of cells from the animal hemisphere, so that upper micromeres begin to migrate over the edge of the dorsal lip and roll inside and are tucked beneath the cuter age.
B.Overgrowth, when the micromeres divide rapidly and begin to spread downwards over the metameres except at the yolk plug.
C.Rotation of gastrula within the vitelline membrane, so that the animal pale becomes anterior.
D. Formation of a small slit-like invagination occurring on the grey crescent.

Answer 1

Hint: Gastrulation is a phase in the embryo development in animals. In this stage, blastula develops into gastrula. Whereas, epiboly is one of the cell movements that occur in the early embryo during gastrulation.

Step by step answer: In the process of epiboly, the outer layer of cells becomes radial and starts to move towards the blastopore. In this process, the cells of the blastula which will become the mesoderm and endoderm, are arranged beneath a layer of cells, which then becomes the ectoderm. It is the overgrowth when the micromeres divide rapidly and begin to spread downwards over the metameres except at the yolk plug.
i. The formation of the gastrula not only involves cell division but the arrangement of cells is also important. The arrangement of cells is done by the movement of cells along the specific paths which are known as morphogenetic movements. These movements are listed below:
i. Progression includes the development of three layers from a solitary layer to change into the gastrula. ii. Invagination: This component occurs in the other piece of the side of the equator, for example, the vegetal shaft where the outside sheet of cells begins to move inside the blastula.
Thus, the correct answer is option B.

Note: Gastrulation spots the point in progress that the internal cells are separated from the cells that will cooperate with the environment. The archenteron, or gut, produces during gastrulation. The singular opening to the gut is called the blastopore. In jellyfish, it acts as both the mouth and the anus. In higher animals, a second notch develops during the arrangement of the internal organs.