Gastrulation in some Animals
As mentioned before gastrulation marks the beginning of morphogenesis that is development of body form and organisation of cells in the embryo. By the end of this process the groups of cells destined to make different tissues and organs are arranged in their relevant proper positions within the three germinal layers (ectoderm, mesoderm, and endoderm) and the primitive basic body plan of the animal is recognized.
Though, in different groups of animals gastrulation occurs in different ways ascertained mainly by the type of egg and subsequent pattern of cleavage and the structure of blastula. You will study gastrulation as it takes place in echinoderms amphibians, birds and eutherian mammals. The description will help you to understand the difference in the method of gastrulation because of the effect of the amount of yolk and pattern of its distribution in the egg, subsequent pattern of cleavage and the final structure of the blastula.