Anatomical, physiological, biochemical and behavioral studies will be carried out on the peripheral auditory system of bats of the genus Pteronotus. These bats emit intense ultrasonic pulses that contain a harmonic series of frequency modulated and constant frequency components. The comparative structure of their pulses will be examined with a new phase-locked loop device capable of resolving instantaneous ultrasonic frequency shifts as small as 20 HZ. The comparative acoustic behavior of these bats will be studied under natural conditions, especially during insect pursuit and capture. Cochlear microphonic potentials will be recorded from flying animals with the aid of miniaturized telemetry systems. The comparative fine structure of the cochleae will be examined with the aid of TEM, SEM and light microscopy. Particular attention will be directed toward: (1) the identifcation, analysis and description of an unusual, thick lining of the scala tympani in Pteronotus parnellii; (2) ultrastructural studies of different cell types in the organ of Corti with attention directed to specialized regions of the cochlea; (3) investigation of evidence indicating that some of the cellular elements of the organ of Corti may contain contractile proteins; (4) the possible physiological significance of these contractile proteins; and (5) the effects of ototoxic drugs on the audiogram, acoustic behavior and ultrastructure of the sharply tuned ear of Pteronotus parnellii.