Formation of large micro-ornamentations in developing scales of agamine lizards.

The embryonic scales of two Australian agamine lizards (Hypsilurus spinipes and Physignatus lesueuerii) derive from the undulation of the epidermis to form dome-shaped scale anlage that later become asymmetric and produce keratinized layers. Glycogen is contained in basal and suprabasal cells of the forming outer scale surface that are destined to differentiate into β-keratin cells. The outer peridermis is very flat, but the second epidermal layer, provisionally identified as an inner peridermis, is composed of large cells that accumulate vesicular bodies and a network of coarse filaments. The sequence of epidermal layers produced beneath the inner peridermis in these agamine lizards corresponds to that of previously studied lizards, but the first subperidermal layer has characteristics of both clear (keratohyalin-like granules) and oberhautchen (dark β-keratin packets) cells. This layer is here identified as an oberhautchen since it fuses with the underlying β-keratinizing cells forming large spinulae as the entire tissue becomes syncytial so that the units appear to increase in size. These spinulae very likely represent sections of honeycomb-shaped micro-ornamentations. A mesos layer appears underneath the β-layer before hatching. J. Morphol. 240:251-266, 1999. © 1999 Wiley-Liss, Inc.