Gregory's diverticulum is a conspicuous digestive tract element found in selected sand dollar (Echinoidea: Clypeasteroida) species. This organ, a transitory structure of the juvenile organism, was named after the American zoologist Emily R. Gregory (1863–1946). Although it had been observed before by the renowned echinoid researcher and former director of the Museum of Comparative Zoology Alexander E. Agassiz, Gregory was the first to describe the organ as a distinct entity on the basis of the ubiquitous sand dollar species Echinarachnius parma. However, despite presenting her discovery at several national and international conferences, as well as in short papers, Gregory's find remained largely unmentioned by contemporary echinoderm researchers. With the erroneous assessment of one of the most eminent authorities on echinoid taxonomy and systematics Theodor J. Mortensen that the organ she discovered does not exist, Gregory's work seemed destined to fall into oblivion. However, in the second half of the 20th century, several unpublished master's theses provided unequivocal evidence for the existence of the organ, thus reviving interest in research on Gregory's diverticulum. The present article gives a historical overview of studies related to Gregory's diverticulum, provides the first comprehensive biography of Emily R. Gregory, describes the circumstances of the organ's discovery, and explores why the research of a female zoologist was seemingly not met with much enthusiasm during her lifetime.