Fig. 7. Germ plasm and germ cells during the life cycle of chaetognaths. During oogenesis (1), germ plasm/nuage material (in green) is within and around the germinal vesicle (GV). During maturation and internal fertilization at the vegetal pole (2), germ plasm presumably fragments into minute granules. After spawning (3), many small granules line the vegetal cortex (V) and then aggregate during amphimixy (4). At mitosis (5), small germ granules aggregate into a single large granule. This large granule is segregated into one of the first two blastomeres and continues to be inherited by only one vegetal blastomere until the 32-cell stage (7). The germ granule then fragments and is distributed into two blastomeres at the 64-cell stage (8). The germ plasm is then found in the four presumptive PGCs at the tip of the archenteron in the gastrula (9). The four PGCs become the male (posterior) and female (anterior) germ cells in the juvenile (10), which give rise to the spermatocytes and the oocytes in the adult.