1. B. Källén, in Organogenesis (R. L. DeHaan and H. Ursprung, eds.), pp. 107–128, Holt, Rinehart and Winston, New York (1965).
2. R. L. Watterson, in Organogenesis (R. L. DeHaan and H. Ursprung, eds.), pp. 129–159, Holt, Rinehart and Winston, New York (1965).
3. R. Levi-Montalcini, Events in the developing nervous system, Progr. Brain Res.
4:1–29 (1964).
4. P. Weiss (ed.), Genetic Neurology, University of Chicago Press, Chicago (1950).
5. W. Bloom and D. W. Fawcett, A Textbook of Histology, 8th ed., p. 33, Saunders, Philadelphia (1962).