||P.74 left column bottom paragraph:"The adult wings of Drosophila are derived from imaginal discs that are specified during embryogenesis and proliferate throughout larval development (also called the imago stage) to expand from approximately 50 to 50,000 cells, a thousand-fold increase, over the course of five days ( Fig. 1A and B). This developmental period covers three sequential instars or moltings that occur during larval development [ref 27], [ref 28] and [ref 29]. The wing imaginal disc consists of an epithelial monolayer sac with a lumen." See Morata & Herrera 2010 PMID 20224294 p.226 right column bottom paragraph:"It
was found that [the wing disc] grows essentially during the larval period, starting at the end of the first instar and finishing shortly after the initiation of pupariation. The initial number of cells was about 40–50 and the final number about 50,000. Assuming that all cells contribute equally to the final disc, it would mean that each cells contributes with 1,000 cells to the final structure through about 10 divisions." See Matamoro-Vidal et al. 2015 PMID 25619644 p.1060 right column 2nd paragraph:"The wing is derived from a precursor group of ~30 cells that invaginates from the embryonic ectoderm. This occurs in the anterior/mid-part of the embryo, at the boundary between the second and third parasegments (the parasegments are sections of the ectoderm established along the whole anterior–posterior axis of the embryo) (Bate & Martinez-Arias, 1991). These cells form the wing imaginal disc, a mono-layered sac of epithelial cells that will undergo growth and patterning during the larval stages (Figs. 2, 4)."