Fissure Basalts and Ocean-Floor

closed system grossly distorted sound calibration below 1 khz, whereas at frequencies higher than 6 khz calibration for the open loudspeaker was affected. This difficulty could be avoided by placing the loudspeaker close to the bird's ear (12 cm). 2. R. L. Boord and G. L. Rasmussen, J. Comp. Neurol. 120, 463 (1963). 3. For this reason, all data on single-unit thresholds and frequency range in this paper were obtained from the nucleus angularis. 4. N. Y.-S. Kiang, Discharge Patterns of Single Fibers in the Cat's Auditory Nerve (M.I.T. Press, Cambridge, Mass., 1966). In birds, variation in thresholds among units having similar best frequencies is partly due to experimental conditions. Brain pulsation due to respiration and circulation often made the threshold measurement unreliable. Preparations devoid of this and other conditions, such as bleeding, showed narrower ranges of variation in the thresholds of single units with similar best frequencies. The distribution of best frequencies from such preparations was rather consistent from individual to individual, thus allowing the use of data from a single bird to represent its species. 5. R. J. Dooling, thesis, St. Louis University (1969); , J. Mulligan, J. Miller, in preparation. 6. J. E. Trainer, thesis, Cornell University (1946). 7. I have tried to record as many calls as possible for each species, but I cannot claim to have collected all the vocalizations. The logarithmic intervals on the spectrogram do not match with those on semilogarithmic paper for the entire frequency range. When calls and song consist of repetitions of the same or similar sounds, only one element is shown in the figure. No song was recognized in the sparrow. 8. A tabulated summary of previous work is found in J. Schwartzkopff, Auk 72, 340 (1955). 9. E. G. Wever, Ann. Otol. Rhinol. Laryngol. 68, 975 (1959). 10. 0. Granit, Ornis Fenn. 18, 49 (1941); S. Knecht, Z. Vergl. Phzysiol. 27, 1969 (1940); Ph. Wassiljew, ibid. 19, 424 (1933). 11. M. Konishi, Nature 222, 566 (1969). 12. I thank G. A. Manley, P. Marler, J. Palin, and E. G. Wever for their assistance. Supported by NSF grants GB5697 and GB12729.