 The species are moderately sexually dimorphic with males usually being slightly larger, much heavier, and having larger canines than females.The largest difference between the opossum and non-marsupial mammals is the bifurcated penis of the male and bifurcated vagina of the female (the source of the term "didelphimorph," from the Greek "didelphys," meaning double-wombed).Opossum spermatozoa exhibit sperm-pairing, forming conjugate pairs in the epididymis.