He described the spermatozoa of about 30 species, and thought he saw in semen "all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins...And when I saw them, I felt convinced that, in no full grown body, are there any vessels which may not be found likewise in semen."
Describiu os espermatozoides dunhas 30 especies, e pensaba que no seme vira "todos os tipos de vasos grandes e pequenos, tan variados e numerosos que non dubido de que son nervios, arterias e veas...E cando os vin, quedei convencido de que, nun corpo completamente crecido, non hai ningún vaso que non se poida encontrar igualmente no seme."