Fig. 4. Drosophila Malpighian tubule elongation. (A) Malpighian tubules form as evaginations from the hindgut-midgut junction (blue, parts a,b), and first elongate by cell division (parts b,c), and later by circumferential cell intercalation (parts c-e). Anterior is to the left. (B) Cell intercalation reduces the circumference from about eight cells to two cells, while elongating the tubule commensurately. (C) Mesenchymal cells from the visceral mesoderm (orange) intercalate into the primary cells (pc) to form the stellate cells (sc). (A) Adapted, with permission, from Lengyel and Iwaki (Lengyel and Iwaki, 2002); (C) Adapted, with permission, from Jung et al. and Denholm et al. (Jung et al., 2005; Denholm et al., 2003).