as well as other functions such as body temperature), this may explain how scents influence aggressive and mating behavior. For example, in many vertebrates, nerve signals from the brain pass sensory information to the hypothalamus about seasonal changes and the availability of a mate. In turn, the hypothalamus regulates the release of reproductive hormones required for breeding. Some pheromones are detected by the main olfactory system. Animals which possess The vomeronasal organ originated in tetrapods. The functional vomeronasal system is found in all snakes and lizards, and many mammals. Salamanders perform a nose-tapping behavior to presumably activate their VNO. Snakes use this organ to sense prey, sticking their tongue out to gather scents and touching it to the opening of the organ when the tongue is retracted. The organ is well developed in strepsirrhine primates such as lemurs and lorises, developed to varying degrees in New World monkeys, and underdeveloped in Old World monkeys and apes. Elephants transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the prehensile structure, sometimes called a finger, at the tips of their trunks. Painted turtles use this organ to use their sense of smell underwater. Garter snakes – In addition to the main olfactory system, garter snakes also have the vomeronasal system which consists of the vomeronasal organ. The vomeronasal organ plays an important role in some vertebrates with its sensitivity toward chemicals that are related to mating or sensing prey. For example, the snakes use the organ to detect the presence of prey or predator by gathering the chemical cues in the environment through the flicking behavior of the forked tongue. Moreover, garter snakes also use the vomeronasal organ in their pheromone communication as well. Particularly, there should be a distinction made between the odors and vomodors. Odors are chemicals detected by the sensory cells in the nasal epithelium through the process of olfaction. Vomodors are chemicals detected by the sensory cells from the vomeronasal organ through the process of vomerolfaction. Upon entering the lumen of the organ, the chemical molecules will come into contact with the sensory cells which are attached to the neurosensory epithelium of the vomeronasal organ. More importantly, a new research has demonstrated that the vomeronasal organ is necessary in order for garter snake to respond to airborne prey odors, but fail to respond to airborne non-prey odors. In some other mammals the entire