ULTRASTRUCTURAL CONTRIBUTIONS TO AN UNDERSTANDING OF THE CELLULAR MECHANISMS INVOLVED IN LIZARD SKIN SHEDDING WITH COMMENTS ON THE FUNCTIONAND EVOLUTION OF A UNIQUE LEPIDOSAURIAN PHENOMENON

Previous reports on the fine structure of lizard epidermis are confirm ed and extended by SEM and TEM observations of cell differentiation an d the form of shed material from the American anole Anolis carolinensi s. Attention is drawn to two issues: 1) the tips of the spinules arisi ng from the mature oberhautchen are markedly curved; this morphology c an be seen during differentiation; 2) the median keels of scales from all parts of the body show ''naked'' oberhautchen cells that lack char acteristic spinules, but have a membrane morphology comprising a compl ex system of serpentine microridges. Maderson's ([1966] J. Morphol. 11 9:39-50) ''zip-fastener'' model for the role of the shedding complex f ormed by the clear layer and oberhautchen is reviewed and extended in the light of recent SEM data. Apparently periodic lepidosaurian slough ing permits somatic growth; understanding how the phenomenon is brough t about requires integration of data from the organismic to the molecu lar level. The diverse forms of integumentary microornamentation (MO) reported in the literature can be understood by considering how the ce llular events occurring during the renewal phase prior to shedding rel ate to the emergence of the form-function complex of the beta-layer, w hich provides physical protection. Issues concerning the evolutionary origin of lepidosaurian skin-shedding are discussed. (C) 1998 Wiley-Li ss, Inc.