Answer
Gastrulation transforms a bilaminar embryonic disc into a trilaminar embryonic disc.
Work Step by Step
Gastrulation begins about 15 days after fertilization. The three layers of the gastrula are ectoderm on the outside, endoderm on the inside, and mesoderm in the middle. The ectoderm and endoderm consist of epithelial cells ; the mesoderm is comprised of connective tissue cells derived from mesenchyme. The endoderm will give rise to the epithelia of the GI, respiratory and other systems; mesoderm will form muscles, bone, connective tissue, and peritoneum; ectoderm will give rise to epidermal and nervous tissues.
