Ovary of the southern hairy-nosed wombat (Lasiorhinus latifrons): its divergent structural organisation.

The organisation of the ovarian interstitial tissue in the southern hairy-nosed wombat Lasiorhinus latifrons was investigated. Unlike in most other marsupials, the outer cortical region of the ovary contains abundant luteinised interstitial tissue that largely occurs in discrete lobules, many of which contain a localised area of non-cellular, highly eosinophilic and periodic acid-Schiff-positive material. The findings suggest that the latter arises from the zona pellucida that surrounded the oocyte in growing follicles and that the luteinised interstitial tissue thus developed from transformed theca interna of degenerated atretic follicles. It is hypothesised that this tissue synthesises and secretes progestogens, which may result in the long, and variable, oestrous cycle length that has been found to occur in this species.