The is a critical extra-embryonic membrane found in the embryos of reptiles, birds, and mammals that primarily functions in waste storage and gas exchange . In egg-laying species, it acts as a repository for nitrogenous waste and works with the chorion to facilitate respiration, while in most mammals, it evolves to form the structure of the umbilical cord. 1. Evolutionary Significance and Structure
As human gestation progresses, the allantois undergoes a transformation: allantois
: The allantois and yolk sac are incorporated into the connecting stalk to form the umbilical cord. The is a critical extra-embryonic membrane found in
The allantois is one of the four essential membranes of the —an evolutionary milestone that allowed vertebrates to transition from aquatic to terrestrial environments. It originates as a hollow, sac-like diverticulum from the hindgut (posterior region) of the embryo. While its fundamental purpose is life support, the
While its fundamental purpose is life support, the specific role of the allantois varies significantly between species: