Homozygous embryos show a spectrum of developmental defects. Some embryos form the normal number of segments but have severely compressed ventral denticle belts, indicating that head involution is defective. Some embryos lack some denticle belts and have misplaced filzkorper, indicating defects in head involution and germ-band retraction. The sclerotised mouthparts sometimes show chaotic positioning. The posterior spiracles are sometimes found in the middle of the embryo. Failure of dorsal closure and stalling of gut development are seen in mutant embryos. Some embryos show degeneration or general thinning of the central nervous system (CNS), while in others the CNS appears largely normal except for a constriction at parasegment 10. This constriction is progressive and eventually results in the complete scission of the ventral nerve chord. Cells associated with the constriction are seen to undergo apoptosis. Mutant embryos in which dorsal closure has failed have abnormal actin patterns, with severe disruptions of the leading edge cells. Mutant embryos show widespread ectopic apoptosis compared to wild-type embryos.