Mesoderm becomes: The mesoderm forms skeletal muscle, bone, connective tissue, the heart, and the urogenital system. Due to the evolution of the mesoderm, triploblastic animals develop visceral organs such as stomachs and intestines, rather than retaining the open digestive cavity characteristic of diploblastic animals.
Endoderm becomes: The endoderm produced during gastrulation will form the lining of the digestive tract, as well as that of the lungs and thyroid.
Ectoderm becomes: After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system. During neurulation, ectoderm differentiates into two parts. The first is the surface ectoderm, which gives rise to tissues on the outer surface of the body like epidermis, hair, and nails.
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