his eponymous legacy are the graafian (or ovarian) follicles. he himself pointed out that he was not the first to describe them, but described their development. from the observation of pregnancy in rabbits, he concluded that the follicle contained the oocyte, although he never observed it. the mature stage of the ovarian follicle is called the "graafian follicle" in his honour, although others, including fallopius, had noticed the follicles previously (but failed to recognize its reproductive significance). the term "graafian follicle" followed the introduction of the term "ova graafiana" by albrecht von haller who like de graaf still assumed that the follicle was the oocyte itself, although de graaf realised the ovum was much smaller. the discovery of the human egg was eventually made by karl ernst von baer in 1827. de graaf's contemporary jan swammerdam confronted him after his publication of "demulierum organis generatione inservientibu" and accused him of taking credit of discoveries he and johannes van horne had made earlier regarding the importance of the ovary and its eggs. de graaf issued a rebuttal but was affected by the accusation.