Practice question

Hans Driesch in 1891 separated blastomeres of two-cell and four-cell sea urchin embryos by vigorous shaking in calcium-free seawater, each surviving blastomere subsequently developed into small but complete pluteus larvae with gut, skeleton and ciliary band. This disproved preformationist mosaic theory of Roux and demonstrated each early cell retains totipotent developmental potential, forming any lineage depending on interactions and position. Driesch termed embryos harmonious equipotential systems where parts adjust to regenerate whole. Results established principle of conditional specification and regulative development, founding concepts of morphogenetic fields and embryonic regulation central to deuterostome embryology.