The development of the ovary from birth to maturity in the bank vole (Clethrionomys glareolus) and the vole (Microtus agrestis)

Abstract The postnatal development of the ovary in the bank vole and vole was investigated in order to determine whether the earlier onset of puberty in the vole coincides with a difference in the speed of gonadal development during the immature period in the two species. The ovarian development differed in three respects: in the vole 4–10% of the germ cells are still oogonia when the animal is born, while in the bank vole oocytogenesis is completed during the embryonic period. Follicles develop earlier and more rapidly in the vole than in the bank vole. The early appearance of fluid accumulation in the follicles and the formation of “fluid sacs” in the vole ovary is characteristic.