Physiology of Olfactory System.—The sense of smell is of vital importance in the lives of most of the members of the animal kingdom, for it is primarily connected with the search for food. Seydell1 reviewed this function in some of the lower animals:
Coelenterata: Water hydra react to mechanical and chemical stimuli brought into contact with their tentacles, causing movements of the tentacles and the mouth slits.
Vermes: Worms also have an acute sense of smell. Only the head is sensitive to odors.
Insects: The olfactory end-organs in insects are probably located in the antennae; insects themselves produce odors for a variety of purposes.
Butterflies: These have the enticing odor developed to its highest degree.
Ants: Each ant hill, or colony, has its individual odor. If an ant from one hill is placed in another, it will be destroyed immediately, but if the antennae of the ants in this hill