The ultrastructure of developing wings in the giant silkmoth, Hyalophora cecropia. II. Scale-forming and socket-forming cells

In wings of the giant silkmoth, Hyalophora cecropia, scale-forming and socket-forming cells are first observed on day four of pharate adult development. Scale-forming cells appear synthetically active when they are first observed, for their basal region is filled with huge stacks of polyribosome-studed lamellate endoplasmic reticulum, numerous Golgi complexes containing secretory vesicles and many elongated mitochondria. During later development, some of these organelles diminish in number. Neck and scale regions are predominantly filled with longitudinally oriented microtubules and microfibril bundles, suggesting that their function is one of transport rather than synthesis. The scales originate as finger-like projections of the cell body. They subsequently elongate, flatten out and deposit a cuticle which has a surface differing somewhat from that in other lepidopterans. It consists of longitudinal ridges (1.8-2.4 μ apart), transverse ribs (0.6-1.0 μ apart) and microribs (0.10-0.13 μ apart). Socket-forming cells produce a socket around the neck region of each scale-forming cell. The socket differentiates into several morphologically distinct regions: an apical fibrillar region, a ribosomal region, a mitochondrial-microtubular region and a basal fibrillar region. The absence of polyribosome-studded lamellae of endoplasmic reticulum and Golgi complexes suggests that its primary function is not biosynthesis but support and protection of the scale.