Studies on Marsupial Reproduction. 4. Delayed birth in protemnodon eugenii desmarest.

Abstract

Previous reports of hypertrophied anterior vaginal canals, which serve as ducts for the reception of spermatozoa, in macropod marsupials, are briefly discussed. These have been considered by earlier workers as spermathecae in which spermatozoa are stored for long periods. In the macropod marsupial Setonix brachyurus Quoy & Gaimard it has been shown that spermatozoa are not stored by the female. Delayed birth in this species is due to the storage (in the uterus of lactating females with young in the pouch) of a quiescent unimplanted blastocyst. A brief redescription of earlier work on Setonix is included. A study has been made of the macropod marsupial Protemnodon eugenii Desmarest, in which the anterior vaginal canals become greatly hypertrophied at oestrus and which, following copulation, become filled with seminal fluid. In spite of the large numbers of spermatozoa present only one egg - that of the current ovulation - is fertilized. There is no evidence of storage of spermatozoa. The occurrence of quiescent unimplanted blastocysts in the uteri of females suckling young in the pouch shows that delayed birth in P. eugenii is strictly comparable with the case of S. brachyurus, and is not due to storage of viable spermatozoa by the female.