Placentation in the garter snake, Thamnophis sirtalis

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 i n 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 df certain dyestuffs, -it appears dialyzing membrane.

The evolution of viviparity: molecular and genomic data from squamate reptiles advance understanding of live birth in amniotes

“…1A) and yolk-sac placentae ( Fig. 1C) with little morphological specialization (Weekes 1935, Bellairs et al 1955, Hoffman 1970, Yaron 1977, Guillette et al 1981, Stewart 1990. In contrast, viviparous skinks of the genera Niveoscincus, Pseudemoia, Chalcides, Eumecia, Mabuya, and Trachylepis exhibit complex chorioallantoic placentae and increasing reliance on placentotrophy (Weekes 1935, Blackburn et al 1984, Ghiara et al 1987, Blackburn 1992, Flemming & Branch 2001, Blackburn & Vitt 2002, Stewart & Thompson 2004, Adams et al 2005, Blackburn & Flemming 2012.…”

“…1A and B) and some form of yolk-sac placenta on the abembryonic pole ( Fig. 1C; Weekes 1935, Hoffman 1970, Guillette et al 1981, Blackburn 1992, Stewart 1992. Both placentae are formed via close appositions of uterine and embryonic tissues, and are defined as epitheliochorial in most viviparous reptiles (Blackburn & Vitt 2002, Adams et al 2005 because the embryonic tissues do not breach or invade uterine epithelia.…”

“…In viviparous species, uterine and chorioallantoic capillaries are closely apposed in the chorioallantoic placenta (Fig. 1A), which likely facilitates the exchange of oxygen and carbon dioxide (Hoffman 1970, Blackburn et al 1984, Stewart 1990, Blackburn 1993a, Blackburn & Vitt 2002, Blackburn & Stewart 2011. The epithelia of uterine and chorioallantoic tissues are also attenuated in some viviparous reptiles to bring capillaries closer together and reduce diffusion distances for respiratory gases ( Fig.…”

“…1A, B and C). Placental transport of sodium and potassium has been reported from every viviparous species studied, regardless of reliance on placentotrophy (Hoffman 1970, Thompson 1982, Stewart 1989, Ramirez-Pinilla 2006, Ramirez-Pinilla et al 2011. In contrast, the only lecithotrophic species reported to exhibit magnesium transport thus far is Eulamprus tympanum (Thompson et al , 2001a.…”

Contribuição à biologia de serpentes da Bahia, Brasil: I. vivíparas

“…Atualmente, existe uma certa di scordância quanto a ovoviviparidade porque não há uma simples retenção do ovo. Estudos do "útero" mostram que parte do epitélio maternal degenera-se permitindo uma comuni cação entre a mãe e o embrião (HOFFMAN 1970) . Uma visão mais abrangente e aceita pelos autores deste trabalho .…”