Weissmann, the son of a classics professor, studied medicine at the University of Göttingen. After his graduation, he served as a surgeon in the Austrian army during the Austro-Italian War of 1859. During a visit to the city of Freiburg-im-Breisgau in 1860, Weissmann took such a liking to the city that he settled there the following year. He joined the medical faculty at the University of Freiburg as a teacher of zoology and comparative anatomy. Weissmann soon persuaded the university to build a zoo and museum, and he became the director of both.

During those early years at the university, Weissmann studied the metamorphosis of insects and the sex cells of hydrozoa. But temporarily in the mid-1860s and permanently in the 1880s, he had to give up using the microscope for his observational experiments because of his deteriorating eyesight. Instead, he concentrated on theory. Like many of...