from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The cavity within the body of all animals higher than the coelenterates and certain primitive worms, formed by the splitting of the embryonic mesoderm into two layers. In mammals it forms the peritoneal, pleural, and pericardial cavities. Also called body cavity.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A fluid-filled cavity within the body of an animal. The digestive system is suspended within the cavity, which is lined by a tissue called the peritoneum.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a cavity in the mesoderm of an embryo that gives rise in humans to the pleural cavity and pericardial cavity and peritoneal cavity
The same kind of coelom-formation as in sagitta was afterwards found by Kowalevsky in brachiopods and other invertebrates, and in the lowest vertebrate -- the amphioxus.
Snails collect their metabolic wastes in the coelom - which has been reduced to a sac surrounding the heart.
It's the adjective of coelom SEE-lum, which Merriam-Webster said is "the usually epithelium-lined space between the body wall and the digestive tract of metazoans above the lower worms," which told me basically nothing.
I decided to see how other major dictionaries handle coelom.
Cardio-coelom: that part of the coelom that forms the pericardium.
Dissepiment: a partition wall: applied to the forming septa separating the coelom-sacs in the embryo; also the thin envelope about the members in obtect pupae.
Coelom-sac: the cavity containing the viscera: in embryology one of a pair of closed sacs, arising in the mesoderm of each segment of the embryo and giving rise to more or less of the coelom of the adult.
Of these divisions of the coelom the first two communicate with the exterior by means of a pair of ciliated pore-canals placed at the posterior end of their respective segments.
There are reasons for supposing that the truncal coelom was at one time provided with pore-canals, but supposed vestiges of these structures have only been described for one genus, _Spengelia_, in which they lie near the anterior end of the truncal coelom.
In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of _Amphioxus_.
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