Middle and inner ear anatomy correlates with neurophysiological responses to a wide range of sound frequencies for species of the Gerbillinae representing generalized, intermediate, and specialized anatomical conditions. Neurophysiological data were recorded from 81 specimens of 13 species representing six genera. Anatomical parameters involved in the process of hearing were correlated with the neurophysiological data to assess the effects of different degrees of anatomical specialization on hearing. The 13 species tested in this manner have graphic curves of auditory sensitivity of remarkably similar disposition over the frequencies tested and to those published for Kangaroo Rats. Ears with anatomical specializations show greater auditory sensitivity.The natural history of the Gerbillinae, particularly the kinds of predators, degree of predation, and habitat is reviewed and utilized to interpret the significance of the degree of auditory specialization in the forms studied and to evaluate the prevailing hypothesis that these specializations enhance the ability of these rodents to survive in open desert situations by detecting and evading predators.The middle ear anatomy of five additional genera and species was also studied. Thus, data on the entire spectrum of gerbilline middle ear morphology provide a n evolutionary sequence. Certain anatomical parameters of the organ of Corti show a degree of specialization parallel to that of features of the middle ear. The morphological changes and possible functional roles of these features are considered.A very high correlation exists for degree of specialization and aridity of habitat, thus specialization increases with increasing aridity. This increased specialization may result from more effective predation in open xeric environments. Auditory acuity for a wide range of low frequency sounds augmented by auditory specialization is hence more advantageous here. There does not appear to be selection for hearing at particular frequencies in this range. The peaks of greatest auditory sensitivity appear to correspond to the resonant frequencies of the different components of the middle ear transformer and cavity.

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Forty-four neoplasms were found at necropsy in 115 gerbils from a colony of wild-caught, and first- or second-generation laboratory-raised gerbils. Ten species of gerbils varying from 24 to 61 months of age were affected. The neoplasms occurred in 18 primary locations and included nine neoplasms previously unreported in gerbils. Unusual neoplasms included several squamous cell carcinomas of middle ear, squamous cell carcinoma of ventral marking gland, and Hodgkin's-like lymphoma. Neoplasms were a significant cause of morbidity and mortality in these aging animals.

Seven populations of wild sheep (Ovis ammon) were studied in northern Iran. Analysis of 34 individuals demonstrated that the eastern populations possess a 2n = 58, including 1 pair of metacentric and 27 pairs of acrocentric autosomes. The 2n for the three western localities is 54, characterized by 3 pairs of metacentric and 23 pairs of acrocentric autosomes. In two intermediate localities animals with the following diploid numbers were collected: 2n = 54, identical to western locality animals; 2n = 55, containing five metacentric autosomes; 2n = 56, containing four metacentric autosomes; 2n = 57, with three metacentric autosomes; 2n = 58, identical to the eastern two localities. The X and Y chromosomes are a large acrocentric and a small biarmed chromosome, respectively, in every specimen. The taxonomy of Iranian wild sheep and several evolutionary factors are considered in the light of these chromosomal data. The nonconformity of currently accepted theories on the origins of domestic sheep with the karyological data now available for wild palaearctic and domestic sheep is discussed.