Anatomical information concerning the inner ear in lower vertebrates is greatly limited. Studies which are available provide diverse information on various aspects of the auditory system, but each deals with usually one or a limited number of species which are not necessarily closely related. In this proposed research, part of the investigation will be an expansion of work on selected species of catfishes to study progressive phylogenetic changes in the morphology, histology and ultrastructure of the inner ear. Although all part of the membranous labyrinth will be investigated, major emphasis will be placed upon the saccule; cellular ocmponents and the overlying otolithic membrane will be loked at in detail. This project will utilize conventional methods of light (LM) microscopy and transmission (TEM) and scanning (SEM) electron microscopy. Micromanipulation of the Weberian ossicles, transverse canal and ultimately structures within the inner ear will be done. The data obtained during the course of this investigation should significantly enhance the knowledge of the vertebrate inner ear, and this information when combined with physiological data will lead to a better understanding of the significance of auditory structures and the relation of these structures to the function of the inner ear in all vertebrates.