1. Garstang, W., Quart. J. Mic. Sci., 72, 51 (1928).
2. Conklin, E. G., J. Morph., 54, 69 (1932); J. Exp. Zool., 64, 303 (1933).
3. Vandebroek, G. (unpublished). See Dalcq, A., “Form and Causality in Early Development”, 37 (Cambridge, 1938).
4. Berrill, N. J., “Essays on Growth and Form” (Oxford, 1945).
5. Willey, A., “Amphioxus and the Ancestry of Vertebrates” (London, 1894).