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A fluid-filled sac- or sausagelike, extraembryonic membrane lying between the outer chorion and the inner amnion and yolk sac of the embryos of reptiles, birds, and mammals. It is composed of an inner layer of endoderm cells, continuous with the endoderm of the embryonic gut, or digestive tract, and an outer layer of mesoderm, continuous with the splanchnic mesoderm of the embryo. It arises as an outpouching of the ventral floor of the hindgut and dilates into a large allantoic sac which spreads throughout the extraembryonic coelom. The allantois remains connected to the hindgut by a narrower allantoic stalk which runs through the umbilical cord. See Amnion, Chorion, Germ layers

The allantois eventually fuses with the overlying chorion to form the compound chorioallantois, which lies just below the shell membranes in reptiles and birds. The chorioallantois is supplied with an extensive network of blood vessels and serves as an important respiratory and excretory organ for gaseous interchange. The allantoic cavity also serves as a reservoir for kidney wastes in some mammals, in reptiles, and in birds. In the latter two groups the allantois assists in the absorption of albumin. In some mammals, including humans, the allantois is vestigial and may regress, yet the homologous blood vessels persist as the important umbilical arteries and veins connecting the embryo with the placenta. See Fetal membrane, Placentation

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A fluid-filled, saclike, extraembryonic membrane lying between the chorion and amnion of reptilian, bird, and mammalian embryos.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Allantoic fluid from virally inoculated embryonated eggs or culture media from infected cells were 10-fold serially diluted in DMEM medium before addition to the wells.
The allantoic fluid was collected aseptically for harvesting NDV in a bio-hazard cabinet with the help of Pasteur pipette in a conical flask while the sediments in test tubes were discarded.
Virus-containing allantoic fluid was harvested and stored in aliquots at -70[degrees]C.
Forty-eight hours after transfection, the cell culture supernatant was inoculated into chicken eggs, and the allantoic fluid was harvested as a seed virus and used the following experiment.
Soliman, "Studies on the physiological chemistry of the allantoic and amniotic fluids of buffalo at various periods of pregnancy," Indian Veterinary Journal, vol.
This may be due to presence of allantoic factors including erythritol, possibly steroid hormones and other substances in the female reproductive tract, especially in the gravid uterus which stimulate the growth of most of the Brucellae (Radolf, 1994).
The pathway by which blattabacteria metabolize uric acid begins with the conversion of uric acid to allantoin, followed by allantoic acid, glyoxylate, glycerate, and finally pyruvate (Donnellan and Kilby 1967).
(32,33) The urachal remnants are residual tissues from the embryonic allantoic stalk connecting the umbilicus and bladder.
Umbilical polyps, with vestigial remnants of omphalomesentric duct and allantoic duct, are an infrequent cause of umbilical discharge.
EtOH-induced increases in taurine and PE levels within chick allantoic fluid have been reported and allantoic taurine and PE levels exceeded serum levels [45].