  A smooth four manifold is of finite type $r$ if its Donaldson invariant
satisfies D((x^2-4)^r)=0. We prove that every simply connected manifold is of
finite type by using the structure of Donaldson invariants in the presence of
immersed spheres. More precisely we prove that if a manifold X contains an
immersed sphere with $p$ positive double points and a non-negative
self-intersection $a$, then it is of finite type with r = [(2p+2-a)/4].
