A large portion of the leading developmental biologists in the United States, both historically and today, have participated in the MBL's Embryology Course as directors, lecturers or students. One draw is the Woods Hole location and the availability of marine organisms, particularly the sea urchin, that are ideal for embryological analysis because they shed nearly transparent eggs which are fertilized and develop externally. In the first decades after the course was founded in 1893, its faculty pioneered research directions that remain central today, including the study of cytoplasmic localization in eggs; embryonic cell lineage (important in modern stem cell research); and evolutionary developmental biology (today called ‘evo devo'). Some distinguished embryologists who have directed the course are: