Cell cycle analysis in developing cercariae of Trichobilharzia ocellata (Trematoda: Schistosomatidae).

Cellular proliferation has been analyzed during cercarial development of the digenetic trematode Trichobilharzia ocellata. Prior to the tail-bud stage (about 1,000 cells), cells were actively involved in cellular proliferation. The mean cell cycle was 15.2 hr. The time for mitosis was 1.6 hr; for G1, 5.6 hr; for G2, 3.2 hr, and for the S phase, 4.8 hr. Beginning with the tail-bud stage, an increasing proportion of cells accumulate in the G1 phase. Cytological evidence of changes in the amount of cytoplasm per cell revealed that these noncycling cells were differentiating. During organ development and differentiation, the proportion of proliferating cells decreases and by the 2,000-celled stage proliferation ceases. Our results do not support a germinal lineage theory of cercarial development since none of the observed nuclear types could be unequivocally identified as belonging to the germ line.