Mutant larvae show greatly delayed larval growth. The mutant larvae die stochastically after hatching but some can be maintained in the presence of a yeast food supply for eight days or longer. The mutant larvae undergo little or no growth and none appear to undergo the first moult to the second instar stage. The mutant larvae have no obvious behavioural defects, although some can appear sluggish. Embryos derived from females carrying homozygous germline clones show numerous nuclear fusions between nonsister nuclei at telophase of cycle 13. After fusion, these nuclei drop back into the yolk, often leaving behind free centrosomes. This results in the formation of large multinucleate cells just prior to cellularisation (cycle 14). Actin caps appear to form normally above interphase nuclei in the mutant embryos, however, during metaphase, gaps in the metaphase furrow are common (and are most often found at regions of the metaphase plate most distant from the centrosomes). At the onset of cellularisation, the normally regular actin network is highly disorganised, and in some areas is completely absent, resulting in the formation of multinucleate cells. Centrosome duplication and separation occur normally in the late syncytial divisions of the mutant embryos. However, the relative position of the centrosome pairs on neighbouring nuclei is abnormal. In metaphase mutant embryos, mitotic spindles are often found in parallel arrays, due to the abnormal positioning of neighbouring nonsister centrosomes in early interphase.