Imaginal discs responsible for:
Imaginal discs are monolayer epithelial sacs invaginated during embryogenesis, proliferating throughout larval instars as diploid precursors held undifferentiated by ecdysone and juvenile hormone balance. At pupariation, ecdysone pulse triggers disc eversion, elongation, and differentiation into adult external structures: wings, legs, eyes, antennae, halters, genitalia. They do not contribute to embryonic segmentation, larval cuticle, or germline, which arises from pole cells. Disc patterning uses conserved morphogens Wingless, Decapentaplegic, and Hedgehog establishing anteroposterior and dor
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Imaginal discs - adult structure precursors patterned by Wg and Dpp.