In the early 17th century, the English physician William Harvey, who studied at Padua with one of Vesalius’s students, became the first to describe the full circulation of the blood through the human body.

Harvey was also interested in embryology, his major work was Exercitationes de generatione animalium (On Animal Generation), published in 1651. He made a significant contribution by suggesting that there is a stage (the egg) in the development of all animals during which they are undifferentiated living masses. A biological dictum, ex ovo omnia (“everything comes from the egg”), is a summation of that concept.

His doctrine of omne vivum ex ovo (all life comes from the egg) was the first definite statement against the idea of spontaneous generation. He denied the possibility of generation from excrement and from mud, and pointed out that even worms have eggs.