Development of the dermis (2): larval stages. Collagenous dermal extracellular matrix accumulates between the basal lamina of the epidermis and the underlying mesoderm cells through larval stages (A-H). In all panels, epidermal ectoderm is to the left, somitic mesoderm/mesothelium is to the right, and the developing dermis is shown at the interface between them. (A, B) show overviews at the indicated stages. White asterisk marks the nucleus of a mesothelial cell derived from the external cell layer. (F) is a detail of (B) that shows the dermis to scale with the other panels. Black arrowhead in E indicates striated collagen fibers, which appear first during mid-larval stages. White arrowheads in (A) and (D) indicate clathrin-coated vesicles. Striped arrowhead in (A) shows rough endoplasmic reticulum in a mesothelial cell derived from the external cell layer. Images are to scale except (B), as indicated, and all sections are transverse; dorsal is up, lateral is to the left and medial is to the right. Stage abbreviations: GS, gill slit; met, early metamorphosis.