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Histology and ultrastructure of the placental membranes of the viviparous brown snake, Storeria dekayi (Colubridae: Natricinae)
Author(s) -
Blackburn Daniel G.,
Anderson Kristie E.,
Johnson Amy R.,
Knight Siobhan R.,
Gavelis Gregory S.
Publication year - 2009
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.10650
Subject(s) - biology , placenta , ultrastructure , fetal membrane , uterus , anatomy , chorioallantoic membrane , allantois , yolk sac , fetus , embryo , microbiology and biotechnology , endocrinology , pregnancy , genetics
The placental membranes of the viviparous brown snake Storeria dekayi were examined following mid‐gestation by means of light microscopy, scanning electron microscopy, and transmission electron microscopy to reveal their structural organization and cytological composition. By Zehr stage 32, the chorioallantoic placenta (allantoplacenta) is established around much of the egg, and a well‐developed omphalallantoic placenta occurs in the abembryonic hemisphere. The allantoplacenta exhibits multiple features that enhance interhemal exchange: the uterus and allantois are well vascularized, the chorionic and uterine epithelia are attenuated, and the shell membrane is vestigial and has begun to degenerate. In the omphalallantoic placenta, the uterine epithelium is enlarged and appears to be secretory. The omphalopleure contains two distinct populations of cells, and shows cytological evidence for absorption. In intermediate areas, regions of omphalallantoic placenta are being transformed into allantoplacenta, through depletion of the isolated yolk mass and reduction in epithelial height of both uterus and omphalopleure. Morphological evidence suggests that the allantoplacenta is specialized for gas exchange, and the omphalallantoic placenta, for maternal secretion and fetal absorption. On the basis of the available evidence, we postulate that this pattern is characteristic of the thamnophine radiation of snakes. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.