|Description||Slide shows four black and white diagrammatic drawings of 'the process of gastrulation in Urodeles.'|
Diagrams are labelled 'a' to 'd'.
Diagrams 'a','b' and 'd' are also each labelled with the numbers '1' to '4'.
Diagram 'c' is labelled with the numbers '2' to '4'.
These labels are explained in the following key: 'Fig. 7. The process of gastrulation in Urodeles, revealed by the movement of intra vitam stain marks placed on the surface of the blastula, as in a. The marks stretch and move towards the blastopore rim. In b mark I has become invaginated; in d only mark 4 is left on the surface; the others have become invaginated and passed forwards, forming the gut-wall, and can be seen by transparency through the epidermis. (After Goerttler, Arch. Entwmech. CVI, 1925, modified.)'