Surgical removal of the thymus gland within 48 hours of birth has no effect upon the numbers of small, medium and large ovarian follicles in Bagg albino strain mice during the first 12 weeks of life. 2. 20% of thymectomised mice more than 12 weeks of age developed ovarian atrophy which included the disappearance of corpora lutea and an overall reduction in all fractions of the follicle population. 3. These results do not support the proposal of Nishizuka and Sakakura that the thymus gland specifically maintains the non-growing, small (primordial) follicle pool in the mouse ovary during post-natal and reproductive life.
