Morphogenesis of placental membranes in the viviparous, placentotrophic lizard Chalcides chalcides (Squamata: Scincidae).

摘要: In the scincid lizard Chalcides chalcides, females ovulate small ova and supply most of nutrients for development by placental means. The yolk is enveloped precocially extraembryonic ectoderm endoderm during gastrula stage, establishing a simple bilaminar sac placenta. shell membrane begins to degenerate at this time, resulting in apposition maternal tissues. A true chorioplacenta has developed early pharyngula as choriovitelline placenta first stages an omphaloplacenta. Although disappears rapidly, omphaloplacenta spreads occupy entire abembryonic pole. cleft not confluent with exocoelom, no omphalallantoic develops. By limb-bud allantoplacenta been established, mesometrial placentome composed interdigitating ridges chorioallantois uterine mucosa. discovery five distinct arrangements species, three which are transitory two have previously recorded reptiles, emphasizes need accounts that specify ontogenetic precise identity composition squamate membranes. Contrary previous interpretations, pattern C. chalcides evolutionarily conservative, despite presence reduced mass cytological specializations nutrient transfer. Our observations indicate substantial placentotrophy can evolve squamates without major modifications morphogenetic patterns. J Morphol 232:35-55, 1997. © 1997 Wiley-Liss, Inc.