Reproduction in females of the feathertail glider Acrobates pygmaeus (Marsupialia)

The anatomy of female reproductive tracts collected from 28 Acrobates pygmaeus (Shaw) is described. The tract differs from that of other small possums of the families Burramyidae and Tarsipedidae by having a prominent septum that divides the left and right sides of the vaginal system for most of its length. A median birth canal occurs at parturition but closes within 3–4 days of birth. In south‐eastern Australia, most female A. pygmaeus produce two litters within the breeding season (July to February). A post‐partum oestrus follows the birth of the first litter and the resulting embryos undergo a period of embryonic diapause. The embryos grow slowly during diapause, until the unilaminar blastocysts become approximately 2.0 mm in diameter, and contain about 2,000 cells. The factors influencing reactivation after diapause remain unclear, since no embryos past the blastocyst stage were found. Post‐partum oestrus may follow the birth of the second litter, but if it occurs, the ova either remain unfertilized or degenerate after fertilization. Females are anoestrus during the non‐breeding season. Corpora lutea in the ovaries seldom outnumber blastocysts in the uteri or teats in the pouch. During diapause they undergo a pattern of growth similar to that of the blastocysts and enter a quiescent phase. Corpora lutea disappear within nine days of birth. The pattern of female reproduction in this species is similar to that of other small possums of the families Burramyidae and Tarsipedidae, but is distinct from those of other marsupials.