The formation of the first epidermal generations and in
particular of the shedding complex in the developing
scales of the lizards Anolis lineatopus and Podarcis muralis
was studied by electron microscopy. The initially
linear and bilayered epidermis turned into symmetric papillae, which
became asymmetric scales. The outer
periderm was more electrondense than the following layer, provisionally
named
‘inner periderm’ but
probably derived from the basal layer. Coarse thick filaments progressively
filled the cytoplasm of the inner
periderm or formed reticulate bodies resembling avian peridermal granules.
Peridermal cells cornified slightly
and could be shed in ovo. From the basal layer various suprabasal epithelial
layers were produced. The first
layer contained keratohyalin-like granules and was identified as a clear
layer. Beneath it a spinulated
(Anolis) or serrated (Podarcis) oberhäutchen
differentiated. The clear and ‘oberhäutchen’ layers constitute
the first shedding complex. The first epidermal layers that were shed consisted
of flaking periderm or
periderm together with the clear layer. The differentiation of a mesos
layer was under way before hatching,
when the epidermal morphology resembled a stage 4–5 of the adult
shedding cycle. Fibroblasts under the
inner side of the scale made few contacts with the basement membrane and
their cytoplasmic elongations
were mostly oriented parallel to the dense lamina. Instead, fibroblasts
under the basal layer of the outer
scale surface (BLOS) made numerous contacts with the basement membrane,
suggesting that more dermal–epidermal interactions take place on
this side of the scale.