Allantois (/əˈlæntɔɪs/; plural allantoides or allantoises) is a part of a developing animal conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.

The allantois, along with the amnion and chorion (other embryonic membranes), identify humans, and other mammals, as amniotes. Other amniotes include reptiles, dinosaurs, and birds. Of the vertebrates, only Ichthyopsidas (fish and amphibians) lack this structure.

Read more about Allantois:  Function, Pathology, Etymology, Additional Images

Other articles related to "allantois":

Reptiloform - Evolutionary History - From Aquatic To Terrestrial Eggs
... The first to evolve was probably the allantois, a sack that develops from the gut/yolk-sack ... A very small allantois is found in modern amphibians ... and the chorion, encompassing the amnion, allantois, and yolk-sack ...
Cloaca (embryology)
... first prolonged backward into the body-stalk as the tube of the allantois but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to ... endodermal cloaca into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward ...
Allantois - Additional Images
... to thirty-three days old Opened uterus with cat fetus in midgestation 1 umbilicus, 2 amnion, 3 allantois, 4 Yolk sac, 5 developing marginal hematoma, 6 ...