Allantois is a part of a developing animal embryo. This sac-like structure is primarily involved in respiration and excretion, and is webbed with blood vessels. It is primarily found in the blastocyst stage of early embryological development, and its purpose is to collect liquid waste from the embryo. Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ... Respiration is the process of exchanging oxygen and carbon dioxide between an organism and its external environment (breathing). ... Excretion is the biological process by which an organism chemically separates waste products from its body. ... The arterial system The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ...

The mouse allantois is the mesodermal precurser to the mouse umbilical cord. The mouse allantois undergoes vasculogenesis to form the mature umbilical artery and vein.

Reference

• Bagnell, C. 2005. "Animal Reproduction". Rutgers University Department of Animal Sciences.