Approximately 20% of mutants die as pharate adults. The mitotic index and proportion of cells at different phases of the mitotic cycle in the brains of homozygous larvae are not significantly different from those of wild type. However, the mutant brains have aberrant mitotic figures in which the chromosomes are scattered apparently randomly through the cell, and there is a significant increase in polyploid mitotic figures compared to wild type. The proportion of these defects are increased in hemizygous larvae compared to homozygous larvae. The mitotic chromosomes are highly condensed in metaphase and anaphase in vih¹ larvae. Spindle poles that lack centrosomes are seen and they are characteristically broad. Homozygous and hemizygous females produce syncytial embryos that fail to develop as a result of mitotic defects; the embryos rarely develop beyond the third nuclear division cycle, and mitotic figures have abnormal mitotic spindles and frequently have a polyploid complement of chromosomes.