54-cell embryo, 635 minutes.

<p>2c¹² and 2c²¹ have just divided; the corresponding cells in the 2d lineage are in telophase, and those in the 2a lineage are between metaphase and anaphase. 2b¹² is in prometaphase, and 2b²¹ has not entered mitosis. Mitoses are beginning in the 3ABC cells, while the left and right daughters of 4d have just divided. The 3c¹ cell is in metaphase. The outline of the 4D cell is not shown in this drawing.