Homozygotes have approximately 80% fewer mitotic figures in third instar larval brains than wild-type larvae. Approximately 35% of the mitotic figures have more than the wild-type set of four chromosomal pairs. 90% of spermatids in fbl¹/fbl² males undergo aberrant cell division and spermiogenesis (postmeiotic spermatid differentiation) is grossly defective. 80% of fbl¹/fbl² primary spermatocytes have spindle abnormalities, with the majority of spindles being multipolar. Anaphase and telophase stages are difficult to define in these testes, due to the severe defects in metaphase spindle organisation. In some less severely affected cells, two asters are seen at a single pole. Despite this lack of aster separation, these cells contain a contractile ring positioned over a central spindle.