allantois

[ uh-lan-toh-is, -tois ]

/ əˈlæn toʊ ɪs, -tɔɪs /

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noun Embryology, Zoology.

a vascular, extraembryonic membrane of birds, reptiles, and certain mammals that develops as a sac or diverticulum from the ventral wall of the hindgut.

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Origin of allantois

1640–50; <New Latin <Greek allantoeidḗs, wrongly taken for plural and given a singular, on the model of words like hērōís (singular), hērōídes (plural)

Words nearby allantois

allanite, all'antica, allantoic, allantoid, allantoin, allantois, alla prima, allargando, all-around, al-Lat, allative

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use allantois in a sentence

The cavity of the allantois, if developed, vanishes completely.
The Works of Francis Maitland Balfour, Volume III (of 4)|Francis Maitland Balfour
This bag is called the allantois, and serves as a sort of lung for the developing chick.
The Meaning of Evolution|Samuel Christian Schmucker
It draws its oxygen and throws off its wastes through the instrumentality of the allantois, which covers it over.
The Meaning of Evolution|Samuel Christian Schmucker
The blood vessels of the allantois take in oxygen and give out carbon dioxide through the porous shell.
The Meaning of Evolution|Samuel Christian Schmucker

The allantois of the chick now gains a new development and an altered function.
The Meaning of Evolution|Samuel Christian Schmucker

British Dictionary definitions for allantois

allantois

/ (ˌælənˈtəʊɪs, əˈlæntɔɪs) /

noun

a membranous sac growing out of the ventral surface of the hind gut of embryonic reptiles, birds, and mammals. It combines with the chorion to form the mammalian placenta

Derived forms of allantois

allantoic (ˌælənˈtəʊɪk), adjective

Word Origin for allantois

C17: New Latin, irregularly from Greek allantoeidēs sausage-shaped, allantoid

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for allantois

allantois

[ ə-lăn′tō-ĭs ]

Plural allantoides (ăl′ən-tō′ĭ-dēz′)

A membranous sac that grows out of the lower end of the alimentary canal in embryos of reptiles, birds, and mammals. In mammals, the blood vessels of the allantois develop into the blood vessels of the umbilical cord.