53.6% of mutants die as larvae, 43.4% as pupae. Extreme allele: larval brain and optic lobes become enlarged and disorganised and the imaginal discs are large and clumped. Discs of mutant larvae transplanted into wild-type female abdomens form large contained tumours, whereas transplanted optic primordia from larval brains form invasive neuroblastomas, which grow rapidly, killing the host within 7-14 days. These tumours can be serially cultured in adult abdomens.