The period from 1935 to 1964 established a dominant germ cell–origin paradigm for ovarian neoplasms, foregrounding histogenesis of endodermal sinus (yolk sac) tumors and the biology of benign cystic teratomas. It linked ovarian tumor development to germ cell differentiation and embryologic pathways, while recognizing metastatic spread to the ovaries from primary gastrointestinal cancers as a key diagnostic and therapeutic consideration. In vitro culture studies of excised ovarian tissue and comparative morphogenesis work provided early platforms for controlled study of development and tumor biology in the ovarian context. Historical Significance: These advances anchored germ cell–origin concepts as central to ovarian cancer research, guiding classification, surgical management, and interpretation of histologic patterns for decades. The period bridged descriptive pathology with embryology and developmental biology, establishing a lasting framework for understanding tumor origin, differentiation, and metastatic behavior in the ovary, and setting a precedent for later mechanistic and translational studies.