Final answer:
The vomeronasal organ (VNO) is the structure through which terrestrial vertebrates detect pheromones. It is located adjacent to the nasal cavity and is particularly sensitive to pheromones, sending signals to the brain that influence emotional and reproductive behaviors.
Step-by-step explanation:
Terrestrial vertebrates detect pheromones using an organ called the vomeronasal organ (VNO), also known as Jacobson's organ. This organ is a tubular, fluid-filled structure that is highly sensitive to pheromones and is situated adjacent to the nasal cavity. Pheromones dissolve in the nasal mucosa and enter the VNO, where they bind to specialized receptors. Signals from these receptors are then sent to the brain, specifically to the amygdala, which is involved in emotional responses, and onward to the hypothalamus, which is key to reproductive physiology and behaviors. For example, in a male snake, pheromones secreted by a female can lead to the flehmen response - a curling of the upper lip that facilitates the transfer of pheromone molecules into the VNO.