Fig. 3. Sections of larvae illustrating the development of the imaginal notum. (A) A section through a second instar larva, part of which is enlarged in B, showing the leg and wing buds and a small patch of thickened epithelial cells (imaginal cells) at the junction between the larval epithelium and the wing bud. The notum is derived from this structure. (C) Section through a fourth instar larva. The wing and leg buds have evaginated and lie flat against the body wall. (D) An enlargement of the dorsal area of this section at the level indicated. The imaginal epidermis (star) has replaced the larval one and dorsal closure is complete. Remnants of the degenerating cells of the larval epidermis can be seen as small black spots (arrowhead).

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