The Determinant for Archenteron Formation in Starfish: Co‐Culture of an Animal Egg Fragment‐Derived Cell Cluster and a Selected Blastomere

A method of detecting blastomeres that carrying the determinant for archenteron formation was established, based on the reported localization of the determinant in the vegetal cytoplasm (17, 24). The essence of the method was to co-culture a selected blastomere with an animal egg fragment-derived cell cluster, so as to generate one joined embryo. The presence of the determinant in the blastomere was assessed by the formation of the archenteron in the developed joined embryos. The vegetal blastomeres that carried the determinant sometimes induced animal egg fragment-derived cells to form part of the archenteron.