Abstract:[Objectives] The olfactory and vomeronasal organs are present and well developed in squamates (lizards and snakes). To elucidate the evolution of chemoreception in reptiles, a detailed structural examination of the vomeronasal organs from a variety of squamate species is required. [Methods] The histological features of the nasal cavity and vomeronasal organ in Phrynocephalus frontalis,P. przewalskii, Eremias multiocellata and Scincella tsinlingensis wereexamined using hematoxylin-eosin staining. The data was analyzed using one-way Analysis of Variance with Duncan’s method for multiple comparisons between species. [Results] The nasal cavity of P. frontalis is long and narrow, while the nasal cavity of S. tsinlingensis is pear-shaped; in contrast, the nasal cavity of other two lizards are slightly round (Fig. 1). The olfactory epithelium of S. tsinlingensis is the thickest, followed by E. multiocellata and P. frontalis, and the olfactory epithelium of P. przewalskii is the thinnest (P < 0.05) (Fig. 2 and 3). The vomeronasal organ is composed of the vomeronasal lumen, vomeronasal sensory epithelium, vomeronasal nerve and mushroom body. No glandular structures were found in the vomeronasal organ. The vomeronasal lumens of P. frontalis and P. przewalskii are broader than E. multiocellata and S. tsinlingensis. The vomeronasal sensory epithelium is thicker than the olfactory epithelium in four species of lizards. At the caudal portion of the vomeronasal organ, the mushroom body disappears and the vomeronasal sensory epithelium entirely lines the circular lumen of the vomeronasal organ. The vomeronasal sensory epithelium is situated dorsally to the vomeronasal organ in E. multiocellata and S. tsinlingensis, while the mushroom body occupies the veutri of the vomeronasal organ; in contrast, the vomeronasal sensory epithelium is situated ventrally to the vomeronasal organ in P. frontalis and P. przewalskii, while the mushroom body occupies the dorsum of the vomeronasal organ (Fig. 1 and 4). At the middle region of the vomeronasal organ, the vomeronasal sensory epithelium of E. multiocellata is the thickest, followed by S. tsinlingensis, and the vomeronasal sensory epithelium of two species of Phrynocephalus is thinner. The density of vomeronasal sensory cells of S. tsinlingensis is the highest, followed by E. multiocellata, and the two species of Phrynocephalus are the lowest (Fig. 3). [Conclusion] These results indicate that E. multiocellata and S. tsinlingensis use and invest more in chemical signal than two species of Phrynocephalus. The differential features of the vomeronasal organ from four species of lizards indirectly confirm the specificity of vomeronasal organ phylogeny in squamates.
