1. V. Hensen, Z. Anat. EntwGesch.1, 213 (1875);1, 353 (1876).
2. ‘Nach vorne bildet sich ein scheibenförmiges Ende an ihm aus, welches ich als Knoten bezeichnen werde’, p. 268.
3. The terms ‘epiblast’ (or ‘ectoblast’) and ‘ectoderm’ are in general used synonymously, as well as ‘mesoblast’ and ‘mesoderm’ and, respectively, ‘hypoblast’ (or ‘endoblast’) and ‘endoderm’. I have mainly used the ‘blasts’ when referring to the positions of the layers and the ‘derms’ when speaking of the tissues derived from these layers.
4. J. C. Daniel Jr. andJ. D. Olson, Anat. Rec.156, 123 (1966).
5. F. Peebles, Roux' Arch.7, 405 (1898).