Figure 3. Systematic, gradual germ plasm RNP recruitment to the furrows is followed by the stabilization of germ plasm aggregates in furrows for the first two cell cycles. Microtubules emanate from the sperm monoaster during the first cell cycle (A) reaching the cell cortex where they initiate preaggregation of germ plasm RNPs in an outwardly moving “aggregation front” (B). During cytokinesis for the first (C), second (D), and third (E) cell cycles, RNPs dispersed in the blastodisc cortex are gradually collected by the action of asters from opposite sides of bipolar spindles. The orientation of cell division plane alternates by 90° every cell cycle (double-headed arrow indicates direction of the spindle for each ongoing cell division, which is perpendicular to the plane of division), allowing the collection of RNPs from cortical regions not harvested by the previous cell cycle. Recruited RNPs undergo distal compaction during furrow maturation, resulting in a more compact structure at distal ends of the furrow. RNP clearing results in the depletion of the four RNP aggregates generated during the third cell cycle and any remaining uncollected cortical RNPs, so that subsequent cell cycles (F) contain only the largest RNP aggregates, corresponding to the first and second cell cycle furrows. Furrows for the first (1st), second (2nd), third (3rd) and fourth (4th) cell cycles are indicated (red font indicates actively forming furrow). Furrow maturation generates a mature furrow septum containing newly added membrane and cell adhesion junction components.