1. Airapet’yants, E.Sh. and Konstantinov, A.I., Ekholokatsiyav prirode (Echo Sounding in Nature), Moscow: Nauka, 1974.
2. Alexander, G., Entwicklung und Bau des inneren Gehororganes von Echidna aculeate, Denkschr. Med.-Naturwiss. Ges., 1904, vol. 6, no. 2, pp. 1–118.
3. Babushina, E.S., Zaslavskii, G.L., Krasnitskii, B.Yu., and Yurkevich, L.I., Sensitivity of Hearing in Northern Fur Seal to Changes in Frequency in Aqueous and Air Media, Morskie mlekopitayushchie (Marine Mammals), Arkhangel’sk, 1986, pp. 18–19.
4. Bel’kovich, V.M. and Dubrovskii, N.A., Sensomye osnovy orientatsii kitoobraznykh (Sensory Foundations of Orientation in Cetaceans), Leningrad: Nauka, 1976.
5. Bogoslovskaya, L.S. and Solntseva, G.N., Slukhovaya sistema mlekopitayushchikh (Auditory System of Mammals), Moscow: Nauka, 1979.