| In amniotes, the embryo develops in a blastodisk atop a large yolk mass. |
| At 38 minutes after insemination, the first cleavage was observed and the first cleavage furrow of the blastodisk appeared at 53 minutes. |
| Yolk syncytial nuclei originated from the deepest, open cells beneath the blastodisk. |
| The blastomeres then may be arranged as a saucer-shaped blastodisk covering the blastocoel. |
| Note the blastula in reptiles is called a blastoderm or blastodisk because the divisions have been concentrated into a thin disk of cells at the animal pole. |
