allantois

n. sac-like extraembryonic membrane which develops in certain animals (Zoology)

Allantois (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 allontois, along with the amnion and chorion (other embryonic membranes), identify humans as amniotes, along with reptiles, dinosaurs, birds, and other mammals.
See more at Wikipedia.org...

Noun
1. vascular fetal membrane that develops from the hindgut in embryonic higher vertebrates (reptiles, birds and mammals)
(hypernym) fetal membrane
(classification) mammal

n. allantois, sac-like extraembryonic membrane which develops in certain animals (Zoology)

(n.)
Alt. of Allantoid