Fig. 125.—Diagram to show the Meeting of the Four Tubes in such a Vertebrate as the Lamprey. "Nc.", neural canal with its infundibular termination; "Nch.", notochord; "Al.", alimentary canal with its anterior diverticulum; "Hy.", hypophysial or nasal tube; "Or.", oral chamber closed by septum. (All references in this work to "Ammocœtes" or "Petromyzon" appear to refer to the European Brook Lamprey, now called "Lampetra planeri".)