Abstract
Inception of hearing and opening of eyelids were examined in cat, rabbit, dog and mink. The hearing tests were performed with pure tones and bands of noise observing various types of behavioural responses. Hearing was found to occur at an average age of 5 days in cat, 7 days in rabbit, 14 days in dog and 29 days in mink. The frequencies first responded to and the successive development of hearing for other frequencies are reported and related to data from the literature for five other species. Opening of eyelids started at an average age of 7 days in cat, 10 days in rabbit, 14 days in dog and 33 days in mink. The possible connection between blood supply to the various coils of the cochlea (in man) and the ontogenetic development of hearing and the deterioration of hearing with aging and acoustic trauma is discussed.

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