BIOLOGY OF UNDERWATER HEARING IN AMPHIBIANS.
Final terminal rept. 1 Jan 53-31 Dec 62,
IOWA UNIV IOWA CITY
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Each bronchus of frog larvae forms a distended bulb, capped by fine membrane. From this bronchial membrane ascends a columella which, piercing the dorsal aorta, attaches itself to the round window of the optic capsule. This arrangement serves as a bronchial middle ear, transmitting impulses from aerial vibrations of the lung sacs to the perilymphatic and endolymphatic fluids. At metamorphosis the bronchial middle ear is replaced by the tympanic middle ear, a homologue of the human organ. Though this involves a reversal of the roles of round and oval windows, morphology and function of the inner ear remain the same. Studies in the intricate physiology of the saccular part of the inner ear indicate that the amphibian and basilar papillas are the auditory receptors while the sensory maculae of sacculus and lagena have some little understood hydrostatic functions. In the larvae of Xenopus laevis vibratory impulses from the lungs are directly transmitted to the round windows by airsacs, the bronchial diverticles. Hydrophonic analyses of underwater sound production and hearing in the adult Xenopus show a preferential frequency of about 1700 cps in mating calls. On the other hand in food reward-conditioned reflex testing blinded animals performed best at about 500 cps. The spectrum of hearing spreads from 0 to 5000 cps. Intensive studies were made on morphology and functional capacity of the basilar papilla and on the problem of frequency discrimination. Author
- Anatomy and Physiology