chb⁷ mutant spermatids contain irregularly sized nuclei or multiple nuclei and an enlarged Nebenkern, revealing defects in karyokinesis and cytokinesis, respectively. 32% of chb⁷ mutant spermatocytes exhibited abnormal spindle formation with aberrant central spindles. 60% of chb⁷ mutant spermatocytes exhibit cleavage defects. These include a delay to furrow ingression and aberrant spindle formation, with microtubules remaining associated with the spindle poles as oppose to extending into the equatorial region. This often results in spindle collapse and cytokinesis failure. 73% of chb⁷ mutant spermatocytes form normal peripheral microtubule bundles. The remaining 27% exhibit abnormalities that manifest as an apparent decrease in microtubule probing, or, more often, as a reduction in the robustness of the peripheral microtubule bundles and an instability leading to degradation before cleavage. In contrast to wild-type cells, which consistently form stable interior central spindles, these are found only in 47% of chb⁷ mutant spermatocytes, indicating that chb⁷ cells display defects in central spindle formation, correlating with a failure of cytokinesis. The interior central spindle microtubules are more severely affected than those of the periphery and furrows initiate but then may regress and fail.