  The space of polynomial differential equations of a fixed degree with a
center singularity has many irreducible components. We prove that pull back
differential equations form an irreducible component of such a space. The
method used in this article is inspired by Ilyashenko and Movasati s method.
The main concepts are the Picard Lefschetz theory of a polynomial in two
variables with complex coefficients, the Dynkin diagram of the polynomial and
the iterated integral.
