Final answer:
The substance that covers the kinocilium and stereocilia is the otolithic membrane, which is a crucial part of the inner ear's balance system.
Step-by-step explanation:
The jelly-like substance that covers the kinocilium and stereocilia is known as the otolithic membrane. This gelatinous layer is found in the utricle and saccule of the inner ear. Embedded within the otolithic membrane are tiny crystals made of calcium carbonate, referred to as otoliths. These otoliths add mass to the membrane, making it responsive to gravity and head movements.
As the head moves, the otolithic membrane shifts, which in turn causes the stereocilia to bend. This bending of the stereocilia leads to the depolarization or hyperpolarization of the hair cells, and these signals are interpreted by the brain to determine the position of the head.