  We study the space of arcs on a singularity of the form xy=f(z_1,..., z_n)
and prove 2 main results. (i) The number of irreducible components equals the
multiplicity of f minus 1. (ii) If n>1 and the leading homogeneous term of f is
not a perfect square then the Nash map from the set of irreducible components
to the set of essential divisors is not surjective.
