By Levi Clancy for Student Reader on
Intrinsic (aka cytoplasmic) and extrinsic determinants coexist, as shown by two (respective) urchin blastula experiments.
Removing the progenitor cell of mesoderm from an urchin blastula results in a mesoderm-lacking larva. However, sagittally halving an entire blastula will result in a normal larva. The phenom of extrinsic determinants is known as regulative development.