While its fundamental purpose is life support, the specific role of the allantois varies significantly between species:

: In humans, the allantois is largely vestigial as a sac but remains vital as a structural precursor. Its blood vessels become the umbilical arteries and veins , connecting the fetus to the placenta for nutrient and gas exchange. 3. Developmental Fate in Humans

myesr.org/poster/esr/ecr2020/C-10164/background">urachal cysts or other developmental remnants?

: The intra-embryonic portion of the allantois contributes to the development of the urinary bladder. After birth, it regresses into a fibrous cord known as the urachus or the median umbilical ligament. Summary of Key Roles Species Context Excretion Stores uric acid and nitrogenous waste. Birds and Reptiles Respiration Facilitates gas exchange via the chorioallantoic membrane. Birds and Reptiles Circulation Develops into the umbilical blood vessels. Humans and Mammals Organogenesis Contributes to the formation of the urinary bladder.

: The allantois and yolk sac are incorporated into the connecting stalk to form the umbilical cord.

: It is present in all amniotes, including reptiles, birds, and mammals.

: The allantois is typically small and unattached in most marsupials, though it does fuse with the chorion in specific groups like bandicoots and koalas.

: It is derived from the splanchnopleure, which consists of endoderm and splanchnic mesoderm. 2. Functional Diversity Across Species