The development of the ovary in the wood mouse, Apodemus sylvaticus

The ovary of a young wood mouse, Apodemus sylvaticus, is filled with small follicles, which quickly become atretic. A follicle in an advanced stage of atresia leaves a hole, sometimes with demonstrable remnants of the oocyte or the granulosa cells. The secondary interstitial tissue of the ovaries appears first in association with these holes, possibly developing from the thecal cells. The presence of the secondary interstitial tissue was first observed in seven weeks old females. All the nine week old mice had well developed interstitial tissue.