Hemizygous animals die at the embryonic/first larval instar border. A variable cuticle phenotype is seen, with the severity of the defects correlating with the degree of failure of head involution. The frontal sac appears collapsed, and the pharynx occupies a more anterior position than normal. The salivary glands are missing. Homozygous mutant clones in the head have a mutant phenotype - novel tissue is seen in the postgena and other structures are disrupted.