He divides receptors into three classes— "nociceptors", such as the nerve-endings for pain and hunger, "beneceptors", such as the nerve-endings stimulated when sugar melts on the tongue, and "neutroceptors", such as the nerve-endings in the eye and ear, called " neutroceptors " because they receive more or less indiscriminately both pleasant and unpleasant messages.
Source: wiktionary