Organic transducer made up of a mechanical portion that activates a neural portion. It provides a specific function by reacting only to a certain form of stimuli. Example 1: semicircular canal, which consists of a curved, fluid-filled tube with a flow sensor ( cupula) at one end (mechanical) that activates attached hair cells (neural). It reacts only to angular acceleration (turning) in its plane. Example 2: an otolith organ, which consists of heavy particles (mechanical) that are attached to a bed of hair cells (neural). The direction of inertio-gravitational pull on the heavy particles, and hence the hair cells, provides input as to head position.