The given diagram shows the experiment of embryonic induction performed by Spemann and Mangold.After analysing the result of experiment, the structure that was designated by Spemann asprimary organiser is the

Explanation

In Spemann and Mangold's experiment, the dorsal blastopore lip of the donor embryo was transplanted to the recipient embryo, leading to the formation of a secondary axis, including a second neural tube. This region was designated as the 'primary organizer' because it had the ability to induce the formation of new embryonic structures. The second neural plate and the mesoderm regions opposite to the dorsal blastopore lip are not the primary organizers; instead, they are structures influenced by the organizer's inductive signals.