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allantois Syllabification: al·lan·to·is
Pronunciation: /əˈlan(t)ōəs/

Definition of allantois in English:

noun (plural allantoidesˌalənˈtō-idēz)

The fetal membrane lying below the chorion in many vertebrates, formed as an outgrowth of the embryo’s gut. In birds and reptiles it grows to surround the embryo; in eutherian mammals it forms part of the placenta.
Example sentences
  • The urachus is a remnant of allantoic origin, connecting the embryonal cloaca to the allantois during early intrauterine life.
  • In the fetus, the urachus connects the bladder with the allantois.
  • Initially, the bladder is continuous with the allantois.


Pronunciation: /ˌalənˈtō-ik/
Example sentences
  • We're talking about things like the amnion, the chorion, the allantoic sac, the placenta, the umbilical cord, if those words sound familiar to you.
  • Veterinarians are completing the study comparing allantoic and amniotic fluids and heart rates of fetuses in mares.
  • The embryo forms an allantoic placenta, as is true of at least some peramelids and koalas but not other marsupials.
Example sentences
  • The spores are white, and are cylindrical to allantoid in shape.
  • HvAV - 3a virions vary from allantoid to bacilliform, and are not occluded in occlusion bodies.
  • When screening germ plasm for Karnal bunt resistance, allantoid secondary sporidia produced in solid media should be used as inoculum.


Mid 17th century: modern Latin, based on Greek allantoeidēs 'sausage-shaped'.

Definition of allantois in:
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