From 1920 to 1929 he was director of the zoological institute at Graz.

That same year he became chairman of the zoology department and director of the zoological institute at the University of Münster.

From 1926-1935 he was a professor and director of the zoological institute at the University of Berlin.

From 1971-1972 he worked as a university professor at the zoological institute of the Darmstadt University of Technology.

In 1871 he established the zoological institute at the University of Rostock.

From 1888 he was a professor of zoology at the University of Kiel, where he also served as director of the zoological institute and museum.

At the zoological institute, he served as curator of herpetological collections.

In the years 1949-1952 Jírovec led the Department of Zoology, and later managed a zoological institute.

Afterwards he worked as an assistant to Karl Brandt (1854-1931) at the zoological institute in Kiel.

Unable to think about anything but Lotte, Jakob gives up his job at the zoological institute and devotes himself to finding her.