Brains of mutant larvae do not show defects in the early stages of neuroblast and ganglion mother cell divisions; the cells have regular asters and metaphase figures and they enter anaphase normally. Middle and late anaphases also have a normal appearance. However, telophases have severely abnormal central spindles; in early telophase, the central spindles appear less dense than in the wild type and in middle and late telophase they consist of a thin bundle of microtubules of homogeneous width instead of having the typical hourglass shape of wild-type central spindles. The contractile rings are also defective in the mutant telophases; they appear morphologically normal during early telophase, but in late telophase, most of the contractile rings are poorly constricted and may be discontinuous. Mutant males have very small testes which are devoid of dividing spermatocytes.