Zonal spherical functions on CROSS's and special functions

We find formulas for the eigenvalues of the Laplacian and the zonal spherical functions on all simply-connected CROSS's by a simple method, using the trigonometric formulas of spherical geometry, Hopf fiber bundles, and the results on the spectra of the Laplacian on the total space and on the base of a Riemannian submersion with totally geodesic fibers. We find direct relations of the so-obtained zonal spherical functions to the special functions: hypergeometric finite Gauss series, Jacobi polynomials, and orthogonal polynomials including the ultraspherical Gegenbauer polynomials whose particular cases are given by the Legendre polynomials and the Chebyshev polynomials of the first and second kinds. We point out the relations to the corresponding results by Helgason and Berger with coauthors and give brief information about the method of calculating the spectra of the Laplacian on compact simply-connected irreducible Riemannian spaces and the spectra of the Laplacian on the CROSS's obtained therefrom.