allantois

allantois [ə lan′tō is]

n.

pl. allantoides [al΄ən tō′ə dēz΄] [ModL < Gr allantoeidēs, sausage-shaped < allas, sausage (prob. < dial. allē, garlic, via Oscan * allo < L alium, allium) + -eidēs, -OID]

a membranous pouch with a rich blood supply in the embryos of birds, reptiles, and mammals: it is an organ of respiration and excretion for embryonic birds and reptiles: in mammals it helps form the placenta