|Description||Slide shows four diagrams demonstrating the process of 'invagination and mesoderm-formation in Urodeles'.|
Diagrams are labelled 'a' to 'd'. Diagrams 'b' and 'c' have other labels which are explained in the following key:
'Fig. 4 - Diagrams showing the process of 'invagination and mesoderm-formation in Urodeles. Each diagram is a median sagittal section onto which the mesoderm of one side has been projected. a, Early stage ; the dorsal lip is well advanced, the ventral lip barely indicated, the sheet of mesoderm is beginning to spread forwards from the dorsal and lateral lips. b, The tip of the notochord (Ch) is growing forwards beneath the neural plate; the edge of the mesoderm sheet (p) has extended further forward; a small blastocoel (F) is still visible; K, the front of the neural plate. c, d, Further stages; mesoderm is growing in at the ventral lip; the mesodermal sheet has extended forwards and downwards, and leaves only a small area unoccupied. The paired rudiments of the heart are situated near the growing edge of the mesodermal sheet on each side. (From Vogt, Arch. Entwmech. cxx, 1929.)'