INTRODUCTIONAs this study developed the following objectives were kept in mind: 1) To describe the development of the organ of hearing in the gecko, Gymnodactylus kotschyi (this is a fifth in a series, Evans, '33, '34, '35d, '35 e, dealing with various aspects of the developmental history of Gymnodactylus kotschyi); 2) To establish a correlation between ear structure and social behavior in the gecko; and 3) To extend this correlation to other land vertebrates.Geckos are largely nocturnal or at least crepuscular and this is probably related to their courtship and fighting patterns (Noble and Bradley, '33) which differ markedly from those of diurnal lizards. But both types exhibit a strong territorial urge which causes fighting, as has been shown for geckos (Fischer, 1887) and for the diurnal lizard, Anolis carolinensis (Evans, '35 a, b, c, f).During the entire year, except possibly midwinter, geckos of both sexes give vent to a great variety of chirps and short shrill whistlings. These become more insistant toward evening as they run about searching for insect food. The sounds emitted might vary as conditions of the environment alter. For example, if the room in which the geckos are caged is quiet, the chirps are repeated slowly and are somewhat drawn 187 188 LLEWELLYN THOMAS EVANS out. If, however, a person approaches the cage noisily, the calls change to sharp staccato chirps in a higher pitch.With late spring and summer come the breeding calls. A gecko suddenly emerges from a crevice in the bricks or tiles placed in the cage, chirping repeatedly as it runs across a space and disappears into another hole. Very soon a second gecko replies with a series of sharp chirps as he runs along a passageway, emerges from an opening and continues across the intervening space to enter the crevice into which the first one has gone. Soon after, both emerge running swiftly one behind the other and exchanging chirps of varying pitch as they run. Usually it is the female which begins such a manoeuver and the male is thus enticed to follow by her insistent calling. I have observed such courtship activity countless times among Qymnodactylus kotschyi and Hemidactylus turcicus during the years I have had them in captivity (,28-'35). These details emphasize the fact that the gecko behavior is definitely correlated with vocal expression. This presupposes a receptor organ of extensive development.The alligator makes considerable vocal noise, especially during the mating season (Reese, '15). G. M. Allen (Barbour and Loveridge, '30, p. 776) has described a case of vocal expression in the skink, Mabuya bensonii (Peters), the sounds being a series of bark-like staccato notes. Other reptiles seem capable of emitting only hissing sounds produced by a sudden release of air from the lungs, but these sounds are probably not vocal and are not correlated with a corresponding increase in the length of cochlea.
ACKNOWLEDGMENTS