Mitotic divisions appear normal in mutant ganglion or gonial cells. Mitochondrial aggregation begins in middle and late primary spermatocytes in ms(1)413²/0 males, when nuclei reach full size or somewhat earlier. Meiotic spindles are not seen, and the primary spermatocytes undergo immediate transition to spermatids without accompanying cell division and haploidisation. Cells with condensed chromosomes are rare, and those that are seen have a tetraploid configuration. The spermatid nuclei of the 16-cell cysts (tetraploid) are much larger than normal, with quite long tails and large elongated heads. The nebenkern does not show the normal "onion"-shaped configuration and its derivatives disaggregate during elongation. Many derivatives elongate independently, cytoplasmic microtubules are normal and tend to cluster within the aggregation zone and four abnormal tails are formed per nucleus. The early mitochondrial aggregation is also seen in mid-third larval instar gonads. Males show a shaking behavioural phenotype. They also have a fully extended and shaking proboscis under etherisation.