atlas^Δ homozygotes show spermatogenesis defects, namely accumulation of sperm cells in the base of the testis and, conversely, decreased number of sperm cells in the seminal vesicle. The nuclei of sperm cells appear wider, less condensed and less elongated than in controls (not becoming needle-like); fewer individualization complexes appear associates with nuclear bundles and there are fewer progressed bundles, as compared to controls; all nuclear bundles that progress past the canoe stage show an aberrant "curled" phenotype; occasionally, individual investment cones dissociate from the progressing individualization complexes.