1912 Began his studies on the development of the opossum, while an instructor with the Department of Zoology at the University of Texas.

1925 Interest geared towards the embryology of monkeys and worked with George Corner and his rhesus monkey colony.

Carl Hartman is best known for the research he did with opossums and the reproductive physiology of monkeys and publishing his findings in the Contributions to Embryology. His work with primates led to the discovery of ovulation time and it's relationship to the menstrual cycle, through rectal palpations of ovarian follicles of the macaque monkey. In addition, Hartman produced the material on which Streeter and Heuser based their Developmental Horizons, the first complete embryological series in a primate. Working with George Streeter, Hartman described the histogenesis of the corpus luteum and also studied the development of the primate placenta with G.B. Wislocki. In 1932, Hartman published Studies of the Reproduction of Monkeys, detailing his research with primates. It is obvious to see why he played a central role in the study of reproductive physiology.