| Whether derived from an archenteron or formed by folding of the endodermal sheet, the canal initially does not possess an opening at its anterior end. |
| The greater part of the mesoblast is developed from the walls of the archenteron. |
| In ontogeny the notochord is a derivative of the dorsal wall of the archenteron. |
| It has already been stated that the lateral walls of the archenteron in the tail give rise to muscular cells. |
| The mesoderm then lies immediately beneath the ectoderm, with the endoderm lining the roof of the archenteron, the future gut. |
| In the tail the notochord is shewn at ch, the muscles at m, and the solid remnant of the ventral wall of the archenteron at dd. |
