Formation of Notochord and Somites

The formation of notochord and somites from the transplanted dorsal lip was supposed; these are normally derived from cells of the dorsal lip. Even the formation of gut could be explained because the process of involution of the transplanted dorsal lip would produce a secondary archenteron. But the most surprising feature was the formation of neural tube that is not a derivative of dorsal mesoderm (a tissue that differentiates from cells of the dorsal lip) but is formed from ectodermal cells. Microscopic examination had displayedthat the neural tube had developed from the non-pigmented cells of the host ectoderm that were otherwise destined to develop into belly skin. Based upon these results. Spemann concluded that the dorsal lip material had induced the overlying prospective epidermal ectoderm to become neural tissue. During gastrulation involution of chordarnesodermal (dorsal lip) brings this mesoderm into contact with the overlying ectoderm . This contact induces the ectoderm thatnow becomes determined to develop into neural tissue. The other regions of the ectoderm that do not come into contact with the chord mesoderm develop into epidermis and its derivatives.