The structure of the nasal chemosensory system in squamate reptiles. 1. The olfactory organ, with special reference to olfaction in geckos

The luminal surface of the chemosensory epithelia of the main olfactory org an of terrestrial vertebrates is covered by a layer of fluid. The source of this fluid layer varies among vertebrates. Little is known regarding the r elative. development of the sources of fluid (sustentacular cells and Bowma n's glands) in reptiles, especially in gekkotan lizards (despite recent ass ertions of olfactory speciality). This study examined the extent and morpho logy of the main olfactory organ in several Australian squamate reptiles, i ncluding three species of gekkotans, two species of skinks and one snake sp ecies. The olfactory mucosa of two gekkotan species (Christinus marmoratus and Strophurus intermedius) is spread over a large area of the nasal cavity . Additionally, the sustentacular cells of all three gekkotan species conta ined a comparatively reduced number of secretory granules, in relation to t he skinks or snake examined. These observations imply that the gekkotan olf actory system may function differently from that of either skinks or snakes . Similar variation in secretory granule abundance was previously noted bet ween mammalian and non-mammalian olfactory sustentacular cells. The observa tions in gekkotans suggests that the secretory capacity of the non-mammalia n olfactory sustentacular cells show far more variation than initially thou ght.