(n.) An organ for aerial respiration; -- commonly in the plural.

abdomen anus appendix bellows blind gut bowels brain cecum colon ctenidia duodenum endocardium entrails foregut giblets gills gizzard guts heart hindgut innards inner mechanism insides internals intestine inwards jejunum kidney kishkes large intestine lights liver liver and lights lungs midgut perineum pump pylorus rectum small intestine spleen stomach ticker tripes vermiform appendix viscera vitals works