Follicles were classified as primordial, primary, secondary, or antral (arrow). Primordial follicles had one layer of flattened granulosa cells surrounding the oocyte; primary follicles had a single layer to multiple layers of cuboidal granulosa cells without theca cells; secondary follicles had multiple layers of cuboidal granulosa cells, presence of theca cells and larger size than primary follicles; and antral follicles had a fluid-filled cavity adjacent to the oocyte. Bar = 50 μm (Left). Estimated primordial, primary, secondary and antral follicle counts of fresh and frozen–thawed ovaries on day 10 after transplantation. The total numbers of follicles in frozen–thawed ovaries were significantly decreased compared with the transplanted fresh controls. Data are expressed as the mean ± standard deviation. ***P < 0.001(Right).