<prompt> Endolymph in the inner earIs a filterate of blood serumIs secreted by Stria vascularisIs secreted by Basilar membraneIs secreted by Hair cells  <response>: Endolymph fills the membranous labyrinth and rich in K ions and is secreted by stria vascularis and the dark cells present in the utricle and near the ampullated end of semicircular ducts. Reference Dhingra 6th edition pg-24. 