Vertebrates possess not only the chemical senses of taste and smell, but also an additional chemosensory system mediated by solitary chemosensory cells. This population of cells is not confined to a specialized endorgan but scattered in various epithelia. First seen in fishes, these chemosensory cells are now also described in terrestrial as well as aquatic vertebrates. Here we relate the history of solitary chemosensory cells, their distribution and development. Furthermore, the phyletic origin and continuity of solitary chemosensory cells are discussed as well as their relationship to the taste system.