![]() The latter sections were counterstained with haematoxylin. Sections were stained with haematoxylin and eosin, Masson's trichrome stain or by the periodic acid Schiff (PAS) reaction with and without pretreatment with 1% amylase (Sigma, St Louis, Missouri, U.S.A.) at 37☌ for 30 min. Placental fragments were fixed in 10% formalin in 0.1 M phosphate buffer and processed by standard histological procedures for embedding in paraplast, and then sectioned at 5 μm (automatic microtome, Model RM2155, Leica, Germany). We note that, unlike the trophoblast of the subplacenta, the giant cells often occur in close proximity to maternal blood vessels. Trophoblast giant cells occur close to the margin of the subplacenta and we included these in our analysis. Our findings are consistent with this interpretation, but suggest that hormone secretion is directed towards the fetal circulation. The functions that have been ascribed to the subplacenta include hormone production. Because they bury them singly (scatter hoarding) rather than many in a cache, they are important seed dispersers for a number of tree species. They bury excess nuts and fruits for use when food is scarce. ![]() Agoutis usually sit erect to eat, holding the food in their hands. It is found throughout the forest, where it lives mainly on fallen fruits and nuts. This is a medium sized rodent, larger than a guinea pig and with longer legs. The analysis is based on a description of the placenta of the red-rumped agouti ( Dasyprocta leporina). In this paper we review the structure of the subplacenta and examine possible functional correlates. Beneath this is a structure known as the subplacenta that is unique to the hystricognath rodents. The lobules are separated by interlobular trophoblast that is the counterpart of the spongy layer found in the placenta of other rodents. The exchange area or labyrinth is lobulated, an adaptation that allows an increase in the total exchange area and helps to support the larger fetus at the end of gestation. The hystricognath placenta has a number of distinctive features. This reproductive strategy requires a lower rate of energy consumption and is well suited to an herbivorous diet. The newborn is well developed with open eyes and a full coat of hair. They differ from other rodents in giving birth to precocial young. At this time they were able to capitalize upon the emergence of grasslands for which they were well adapted in a number of ways. The hystricognath rodents (Suborder Hystricomorpha, Infraorder Hystricognathi ) appeared in the Eocene and underwent an extensive radiation in the Miocene. Our findings are consistent with this interpretation, but suggest that hormone secretion is directed towards the fetal circulation rather than the maternal tissues. The functions that have been attributed to the subplacenta include hormone production. Within it the vessels pursue a tortuous course with sinusoidal dilatations and constrictions. The subplacenta is supplied entirely from the fetal circulation. ![]() This is probably the amylase-resistant PAS-positive material identified by histochemistry. The syncytial cytoplasm contains electron-dense granules. Microvilli project into these lacunae from the plasma membrane of the syncytiotrophoblast. The syncytiotrophoblast surrounds an extensive system of lacunae. The basal membrane of these cells is often close to fetal blood vessels. There are prominent intercellular spaces between the cytotrophoblast cells. Clusters of multinuclear giant cells occur in the transition zone between the subplacenta and decidua. Beneath this is found syncytiotrophoblast. In the subplacenta, lamellae of connective tissue support a layer of mononuclear cytotrophoblast cells. In addition, to study the microvasculature of the subplacenta, vessel casts were inspected by scanning electron microscopy Results Placentae were collected from early in midgestation to near term of pregnancy and examined by standard histological techniques, immunohistochemistry and transmission electron microscopy. We here describe the subplacenta of the red-rumped agouti and examine the possible functional correlates of this structure. Beneath them, however, is a structure unique to hystricognath rodents called the subplacenta. These correspond to the labyrinthine and spongy zones of other rodent placentae. Hystricognath rodents have a lobed placenta, comprising labyrinthine exchange areas and interlobular trophoblast.
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