Microtubules from the pole contact the equatorial cortex and bundle there in early phase in homozygous spermatocytes (as occurs in wild-type controls), but the internal microtubules fail to form an organised central-spindle array. The cleavage furrow ingresses only minimally and stalls. Eventually the microtubule bundles that have contacted the equatorial cortex become disorganised and the cleavage furrow regresses.