N. H. Barton and G. Hewitt, “Hybrid zones and speciation,” in Evolution and Speciation, W. Atchley and D. Woodruff, Eds. Cambridge University Press, 1981, pp. 109–145.
LibreCat: https://research-explorer.ista.ac.at/record/4332

G. Hewitt and N. H. Barton, “The structure and maintenance of hybrid zones as exemplified by Podisma pedestris,” in Insect Cytogenetics, vol. 10, R. Blackman and M. Ashburner, Eds. Wiley-Blackwell, 1980, pp. 149–170.
LibreCat: https://research-explorer.ista.ac.at/record/4334