1. Barcroft, J., Danielli, J. F., Harper, W. F., and Mitchell, P. D., Nature, 154, 667 (1944).
2. Barclay, A. E., Franklin, K. J., and Prichard, M. M. L., "The FÅ"tal Circulation" (Oxford, 1944).
3. Jorpes, J. E., Holmgren, H., and Wilander, O., Z. Mikrosk.-anat Forsch., 42, 279 (1937).
4. Mörner (quoted by Krause).
5. Levene (quoted by Krause).