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Amniotic sac. The amniotic sac, also called the bag of waters[1][2] or the membranes, [3] is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shortly before birth. The inner of these membranes, the amnion, encloses the ...
Arête. Striding Edge, an arête viewed from Helvellyn with the corrie Red Tarn to the left and Nethermost Cove to the right. An arête (/ əˈrɛt / ə-RET; French: [aʁɛt]) [1] is a narrow ridge of rock that separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial ...
Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old ...
The shell gland fluid contains very high levels of calcium and bicarbonate ions. The thick calcified layer of the eggshell forms in columns from the mammillae structures, and is known as the palisade layer. Between these palisade columns are narrow pores that traverse the eggshell and allow gaseous exchange. The cuticle forms the final, outer ...
The chorioallantoic membrane (CAM), also known as the chorioallantois, is a highly vascularized membrane found in the eggs of certain amniotes like birds and reptiles. It is formed by the fusion of the mesodermal layers of two extra-embryonic membranes – the chorion and the allantois. [1] It is the avian homologue of the mammalian placenta.
The insect vitelline envelope is the outer proteinaceous layer outside the oocyte and egg. The vitelline envelope, not being a cellular structure, is commonly referred to as a membrane. However, this is a technical misnomer as the structure is composed of protein and is not a cellular component. It varies in thickness between different insects ...
Allantois. The allantois (/ əˈlæntoʊɪs / a-LAN-toe-iss; [1] pl.: allantoides or allantoises) is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote 's conceptus (which consists of all embryonic and extraembryonic tissues). It helps the embryo exchange gases and handle liquid waste.
An approximately 90-year-old snapping turtle named Cedar, that suffered an extreme shell injury from a boat propeller, is stroked affectionately while being treated at the Turtle Rescue League in ...