A large proportion of cia^Z4674 mutant spermatids have one large nebenkern associated with either two or four nuclei of normal size, indicating failure of cytokinesis in one or two of the meiotic divisions, respectively. A small proportion (<2%) of cia^Z4674 spermatids have three nuclei, which may be due to failure of cytokinesis in the first meiotic division, followed by budding off of only one daughter cell in the second meiotic division. During early telophase of cia^Z4674 spermatocytes, there is an actin ring of normal appearance and and a normal central spindle. However, as telophase progresses the actin ring fails to fully constrict and the central spindle either becomes less dense or completely disorganized. The cleavage furrow initiates ~10 minutes after anaphase onset as in wild type, but shows a limited ingression and then regresses leading to a failure of cytokinesis.