Blackburn, D.G. (1999b). Placentas, placental analogues, and fetal nutrition in reptiles and amphibians. Pages 840--847, in Encyclopedia of Reproduction. T.E. Knobil and J.D. Neill, eds. Academic Press, New York.

Abstract: Placentae are organs formed from extraembryonic and parental tissues that help sustain embryos physiologically during their development. In viviparous squamate reptiles, in which the fetus develops to term inside the maternal oviduct, the placental membranes typically accomplish gas exchange and provide water and small quantities of nutrients to the embryo. In certain lizards, placental membranes supply virtually all of the nutrients for embryonic development. Morphological attributes of squamate chorioallantoic placentae correlate with the degree of placentotrophy. Some viviparous species of amphibians exhibit specializations for maternal-fetal nutrient provision that are functionally analogous to placentae. Simple placenta-like structures that function in gas exchange are occasionally found among egg-laying amphibians.

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