  In this paper we consider a cascade system in non divergence form which
models the interaction between two different species, the first one can be seen
as a predator and the other as a prey. Both of them depend on time, on age and
on space. Moreover, the diffusion coefficients degenerate at the boundary of
domain. We study, in particular, null controllability of the system via the
observability inequality for the non homogeneous adjoint problem, which is
deduced by Carleman estimates.
