One of the parts of a holometabolous insect larva that will become a portion of the outside of the adult insect during the pupal transformation.
Comment:
Though inaginal discs are sometimes described as “epithelial sacs”, we do not classify them as such, because an “epithelial sac” is defined in Uberon as being a single epithelium, whereas imaginal discs are made of several epithelia with distinct properties.