1. For a review of the literature up to 1969 seeJ. J. J. Kokkedee:The Quark Model (New York, N. Y., 1969).
2. A review of confinement schemes in bag models is to be found in the lectures ofS. D. Drell:Quark confinement schemes in field theory, Erice Summer School (1975); also SLAC-PUB-1683 (November 1975).
3. For a review of theories with confinement due to the confinement of colour-electric field seeQuark confinement in gauge theories of string interaction, presented byL. Susskind at theInternational Summer Institute in Bonn, 1974, and published inLecture Notes in Physics, Vol.37 (Berlin, 1975).
4. L. Schiff:Phys. Trans.,31 B, 79 (1970);Ann. of Phys.,63, 248 (1971).
5. G. Preparata andN. S. Craigie:Nucl. Phys. (in press).