The two atrial tubes of each zooid remain separate in front but unite posteriorly.
During the above described processes the test remains quite intact, and is not perforated at the oral or the atrial openings.
The oral opening into the branchial sack is directed upwards: an atrial opening is remarkably enough not present.
It contains the whole of the nervous system (ng), which is covered behind by the opening of the atrial tubes (cl).
The atrial cavities in Pyrosoma are clearly lined by epiblast, just as in simple Ascidians.
When the young colony is ready to become free, it escapes from the atrial cavity of the parent, and increases in size by budding.
The nervous system is shewn at n, and at points to an atrial tube.
The gills lead also, as in Ascidians, to another cavity, the atrial chamber.
From the atrial chamber the water flows out into the external world.
In Teleutoscolex there is but one pair of funnels opening into the same segment with the atrial pore.
1570s, from Latin atrium "central court or main room of an ancient Roman house, room which contains the hearth," sometimes said (on authority of Varro, "De Lingua Latina") to be an Etruscan word, but perhaps from PIE *ater- "fire," on notion of "place where smoke from the hearth escapes" (through a hole in the roof). Anatomical sense of "either of the upper cavities of the heart" first recorded 1870. Meaning "skylit central court in a public building" first attested 1967.
atrial a·tri·al (ā'trē-əl)
Of or relating to an atrium.
atrium a·tri·um (ā'trē-əm)
n. pl. a·tri·ums or a·tri·a (ā'trē-ə)
A chamber or cavity to which several chambers or passageways are connected.
Either the right or the left upper chamber of the heart that receives blood from the veins and forces it into a ventricle.
That part of the tympanic cavity that lies below the eardrum.
A subdivision of the alveolar duct in the lung from which the alveolar sacs open.