en mutant embryos lack all Keilin's organs. However enX49/en10 heterozygotes have about one Keilin's sensory hair per embryo and do not show a pair-rule phenotype. enX49/en10 embryos grew in in vivo culture, producing implants containing imaginal discs and all larval tissues. Metamorphosed implants were often characteristic of eye-antenna discs, or sometimes thoracic discs. Tissues derived from the thoracic discs contained only anterior structures.