Early round spermatids in the testes of fwd²/Df(3L)emc-E12 males often contain four (or less often, two) normal-sized nuclei associated with an abnormally large mitochondrial derivative. This suggests a failure of cytokinesis in both or one of the meiotic divisions. Spermatids with one nucleus and a mitochondrial derivative of similar size, suggesting successful meiosis, are rare in mutant males. The nuclei are normal in size in all cells, indicating that karyogenesis is unaffected. Flagellar elongation and nuclear shaping appear morphologically normal in these males. All late-stage spermatids are extensively elongated, although the spermatids within the bundles appear thick and irregularly packed. 99.0% of spermatids in the testes of fwd²/Df(3L)7C males are defective, being derived from one or more defective meiotic and/or mitotic divisions. Spermatids with 4 or 2 nuclei per mitochondrial derivative are often seen, and spermatids with 3 or 8 nuclei per mitochondrial derivative are also sometimes seen. In the majority of fwd²/Df(3L)emc-E12 secondary spermatocyte cells undergoing meiosis II, cleavage furrows initiate and ingress (as occurs in wild type). In 38% of these cells, the cleavage furrows do not persist and the daughter cells fuse back together within 15 minutes. The remaining cells form stable cleavage furrows. In late telophase, aberrant accumulations of F-actin appear in the vicinity of the constricted contractile ring.