Table 1.

Approximate timing of cell divisions in L. variegatus

Cycle	Cells (n)	Duration	Cleavage	Duration
1st	1	1 :11	1st	1 :11
2nd	2	0 :31	2nd	1 :43
3rd	4	0 :31	3rd	2 :14
4th	8	0 :31	4th	2 :45
5th	16	0 :28	5th	3 :13
6th	32	0 :32	6th	3 :46
7th	<64	0 :32	7th	4 :18
8th	<128	0 :44	8th	∼5 :02
9th	<256	0 :58	9th	∼5 :52
10th	<512	1 :23	10th	∼7 :22
11th	<1024		Hatch	8 :03

Average division times (hr:min) were determined from a time-lapse sequence of three embryos from one animal observed at ∼24°C. The division times are likely to vary in different animals and are also dependent on temperature, so that the times shown are meant to convey the general features of division times rather than to document them precisely. The early embryonic divisions are synchronous; but later divisions become less synchronous, particularly after the seventh cleavage: so that the division times for different blastomeres are more variable in the later stages. The total cell numbers are approximate for the later stages because several blastomeres at the vegetal pole withdraw form the cell cycle (Summers et al., 1993).