Practice question

During amphibian gastrulation, invagination at dorsal blastopore lip pulls vegetal endoderm and mesoderm inside blastocoel cavity. As involution progresses, expanding cavity lined by endoderm becomes primitive gut or archenteron. Its roof consists of involuted chordamesoderm that will become notochord, floor and side walls are endoderm destined for gut epithelium. Blastocoel is displaced and ultimately obliterated as archenteron enlarges posteriorly. This new cavity later connects to exterior at blastopore forming anus and mouth secondarily, establishing digestive tract anlage that later differentiates into foregut, midgut, hindgut, and associated organs.