Figure 8

Schematic overview of the 6th division cycle and the initiation of the 7th division cycle in B. longimanus . The four colors represent the quadrants of the 4-nuclei stage, with A - yellow, B - red, C - green, D - blue. A-A” View of the vegetal pole during the 6th division cycle. A The division cycle is initiated in A-, B-, and C descendants and at the same time gc has not divided yet. The direction of bI11 and bI12 adjacent to gc are inclined in this embryo (double arrows). A’ Embryo of 52 cells during the 6th division. A” Embryo of 56 cells during the 6th division in which A and C derivatives are delayed in division. B – B” view of the animal pole of three different embryos of 60 cells. With B’ and B” already starting the next (7th) division cycle. The 7th cycle can be initiated in different quadrants, as shown here for C derivatives (in B’) and for D derivatives (in B”).