Invertebrates (and higher animals<>can be placed<>$$$two groups<>based<>on how they develop as embryos$$$they<>develop<>
He injected one of two cells of a two-cell starfish embryo with antibodies  to myosin, and allowed the embryo to develop to the blastula stage.
Invertebrates (and higher animals) can also be placed in one of two groups based on how they develop as embryos.
Invertebrates (and higher animals) can also be placed in one of two groups based on how they develop as what?