Pregnancy in the lactating pigmy possum, Cercartetus concinnus

Abstract

The reproductive tracts of seven Cercartetus concinnus with pouch young were examined. One female had recently given birth, four were pregnant, and two were in anoestrus. The post-partum female was near oestrus. The ovaries contained corpora lutea and large follicles, and luteal regression was occurring in the uteri. Ovaries of pregnant females contained old corpora lutea and corpora lutea of pregnancy. Blastocysts recovered from the uteri increased in size with age of the pouch young. Corpora lutea of pregnancy out-numbered blastocysts in many females, and blastocysts often out-numbered teats. Ovaries of anoestrous females contained only old corpora lutea. During birth the young pass through a cleft in the connective tissue between the posterior end of the vaginal culs-de-sac and the posterior vaginal sinus. This cleft, the pseudovaginal canal, closes after parturition. The observation that embryos of C. concinnus do not enter diapause contrasts with conclusions previously drawn from circumstantial evidence that the pigmy possum resembled several species of Macropodidae in undergoing embryonic diapause.