Final answer:
Gastrulation is the process during development in which the embryonic disc develops a third layer called the mesoderm and a primitive gut. It leads to the formation of the three germ layers - endoderm, ectoderm, and mesoderm - which give rise to specific organs in the body. The endoderm forms the digestive tract, the ectoderm develops into the outer covering of the body and the central nervous system, and the mesoderm forms muscle tissues, connective tissues, and visceral organs.
Step-by-step explanation:
Gastrulation is the process during development in which the two-layer embryonic disc develops a third cell layer called the mesoderm and a primitive gut. This primitive gut eventually develops into the gastrointestinal tract. Gastrulation also leads to the formation of three germ layers: endoderm, ectoderm, and mesoderm. The endoderm forms the wall of the digestive tract, while the ectoderm covers the surface of the animal and the mesoderm differentiates into various structures between the ectoderm and endoderm.
During gastrulation, a tiny hole called a blastopore develops in one side of the embryo. The blastopore deepens and becomes the anus, and it also forms an opening on the other side that will become the mouth. Whether the blastopore develops into a mouth or an anus determines if the organism is a protostome or a deuterostome.
The germ layers give rise to specific body tissues and organs. The endoderm gives rise to the lining of the digestive tract, the ectoderm develops into the outer epithelial covering of the body surface and the central nervous system, and the mesoderm forms specialized muscle tissues, connective tissues, and most visceral organs.