The wonder of things is the beginning of knowledge, as was already stated by Aristotle, the fIrst embryologist known to history. Embryology has remained a source of wonder ever since. It all starts with the fusion of the female egg and the male sperm. Sperm cells were first described by Antonie van Leeuwenhoek (1632-1723) in 1678, who believed them to be parasitic animals present in the male semen, that had nothing to do with reproduction. Nicolas Hartsoeker (1656-1725), the other discoverer of sperm believed that the entire embryonic individual lay preformed within the head of the sperm, as depicted in his famous homunculus (Fig. 1). The fIrst evidence for the existence of the female egg was presented by Reinier de Graaf (1641-1673), although the egg itself was only described in 1827 by Karl von Raer (1792-1876). The actual fertilization process was observed only a century ago by Herman Fol, a Swiss zoologist.

Hirschprung disease, embryology, neural crest
J.C. Molenaar
Erasmus University Rotterdam
Erasmus MC: University Medical Center Rotterdam

van der Sanden, M.J.H. (1994, February 2). The hindbrain neural crest and the development of the enteric nervous system. Erasmus University Rotterdam. Retrieved from