1. For a discussion of the roots of this idea in Greece of the fifth dentury B. C., see George Sarton, A History of Science, Harvard Univ. Press, Cambridge, 1960, pp. 241256.
2. M. Gell-Mann, Phys. Lett. 8, 214 (1964).
3. G. Zweig, CERN Reports TH. 401 and TH. 412, 1964 (unpublished): and in Proc. of the International School of Physics Ettore Majorana, Erice, Italy, 1964, edited by A. Zichichi; Academic Press, New York/London, 1965, pp. 192234.
4. The quark hypothesis is a natural outgrowth-of the composite-hadron model of E. Fermi and C. N. Yang, Phys. Rev. 76,1739 (1949).
5. H. Lipkin, Phys. Rep. 8C, 173 (1973).