Journal ArticleDOI
Placentation in the garter snake, Thamnophis sirtalis
TLDR
The placental memebranes and uterus of the garter snake, Thamnophis sirtalis, were studied using histological, histochemical, electron microscopic, dye transfer, and radioisotopic techniques.Abstract:
The placental memebranes and uterus of the garter snake, Thamnophis sirtalis, were studied using histological, histochemical, electron microscopic, dye transfer, and radioisotopic techniques. The conceptuses are completely enclosed throughout gestation by a transparent shell membrane which is produced by glandular epithelia in the uterine segment of the oviduct.
Both chorio-allantoic and omphalo (yolk-sac) placentation are observed in this snake. The growth of the extra-embryonic mesoderm takes place in a manner peculiar to placental reptiles, and results in the isolation of the omphaloplacenta from the yolk-sac wall. On the basis of morphology, enzyme histochemistry, and phagocytosis of Trypan blue particles, this structure is interpreted as a site of histiotrophic absorption.
The chorio-allantoic region of placentation is simple in structure. Fetal and maternal capillaries are closely apposed but always separated by layers of uterine and chorionic epithelium and the thin shell membrane. The placental membranes of the garter snake are similar in many respects to those of other live-bearing snakes, but less specialized than most lizard placentate.
Isotopically labelled sodium and glycine are passed to the fetus following maternal injection, the latter at least apparently via the omphaloplacenta. The permeability to iron and phospate is extremely low. On the basis of these results and the selective transfer of certain dyestuffs, it appears that the shell membrane functions as a dialyzing membrane.read more
Citations
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Journal ArticleDOI
The physiological ecology of reptilian eggs and embryos. and the evolution of viviparity within the class reptilia
TL;DR: Eggs of Crocodilia and Chelonia have a pair of egg membranes separating a thick layer of albumen from the calcareous shell, while eggs of oviparous Lepidosauria have only a single shell membrane, upon which relatively small amounts of calcium carbonate are deposited.
Journal ArticleDOI
Convergent Evolution of Viviparity, Matrotrophy, and Specializations for Fetal Nutrition in Reptiles and Other Vertebrates
TL;DR: Quantitative analyses based upon the superimposition of phylogenetic and reproductive data have revealed that viviparity has originated on at least 132 independent occasions among vertebrates, with 98 of these origins having occurred among reptiles.
Journal ArticleDOI
Evolution of vertebrate viviparity and specializations for fetal nutrition: A quantitative and qualitative analysis.
TL;DR: Phylogenetic analyses indicate that viviparity has originated independently in more than 150 vertebrate lineages, including a minimum of 115 clades of extant squamate reptiles, and substantial matrotrophy has arisen at least 33 times in these v Viviparous clades.
Journal ArticleDOI
Structure, function, and evolution of the oviducts of squamate reptiles, with special reference to viviparity and placentation
TL;DR: Cladistic analysis indicates that oviductal features associated with deposition of tertiary egg investments in reptiles reflect evolutionary convergence as well as secondary simplification, rather than a unidirectional trend towards increased specialization.
Journal ArticleDOI
Chorioallantoic placentation in squamate reptiles: Structure, function, development, and evolution
TL;DR: Phylogenetic analyses suggest that placental organs have originated on more than 100 occasions among squamate reptiles, and indicate that three separate lineages have converged on substantial placentotrophy through the evolution of specialized histotrophic placentae.
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TL;DR: The new Pearse bids fair to become the leader, even amongst so notable a collection of books devoted entirely or largely to histochemical techniques.
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Animal Tissue Techniques
TL;DR: Animal tissue techniques, Animal tissue techniques , مرکز فناوری اطلاعات و اصاع رسانی, کδاوρزی