| One of the most interesting features in the elasmobranch development is the formation of the notochord from the hypoblast. |
| This cell group often splits into an upper layer, the epiblast, and a lower layer, the hypoblast. |
| Its walls are formed of splanchnic mesoblast with blood-vessels, within which is a lining of hypoblast. |
| When the egg of Amphioxus is in the blastosphere stage we cannot speak of either an epiblast or hypoblast. |
| Using Lankester's terms epiblast, hypoblast and mesoblast for the embryonic germ layers, Balfour described chick ectoderm and endoderm for the first time in English. |
| Further differentiation produces a thin layer of cells, called the hypoblast, between the inner cell mass and the cavity. |
