From testis to teratomas: a brief history of male germ cells in mammals.

In antiquity, many theories were advanced on reproduction and the functions of the gonads. The male genitalia were called "testes" probably from the Latin word "testis" that originally meant "witnesses", because they provide evidence of virility. Through the first dissection of the seminipherous tubules by Renier de Graaf (1668), the discovery of spermatozoa by Antonj van Leeuwenhoek (1677) and in vitro fertilization by Spallanzani (1780) and later by George Newport and George Vines Ellis (1854), it was only in the early part of the XIX century when it was realized that testes produce spermatozoa and that they are essential for egg fertilization and subsequent embryo development. In the period between the end of the XIX and the beginning of the XX century, scientists such as Albert von Kölliker, Franz von Leydig, Enrico Sertoli and Gustaf Retzius (1842-1919) did microscopic observations of testis that marked the history of male germ cells and established the bases for the development of contemporary in vitro culture and molecular studies that are revealing the deeper secrets of male germ cells. Among these, those by Leroy Stevens on embryonal carcinoma cells in the early 1950s led to the present concepts that germ cells and cancer cells share several characteristics and that a close relationship exists between germ cells and stem cells, these being two pillars of modern developmental biology.