Remnants of the paramesonephric (Müllerian) ducts can be found in the male as a uterus-like structure. Historically, these have been known as a masculine uterus. We examined the reproductive tracts of 24 male North American beaver, Castor canadensis Kuhl, obtained from trappers between 1980 and 1997 from four areas extending across Ontario. Persistent paramesonephric ducts were found in 20 of these tracts. Prevalence was not related to geographic location. Grossly, the remnant appeared as one or two thin, uterus-like tubes medial to the ducti deferentes, with or without a medial corpus lying between the ampullae. Histologically, the paramesonephric remnants resembled a normal female uterus, but the endometrium consisted primarily of amorphous extracellular matrix. Previous descriptions of the prevalence of the paramesonephric duct remnants (male uterus) in C. canadensis were found to be contradictory.
Invasion of North American beaver (Castor canadensis) in the province of Magallanes, Southern Chile: comparison between dating sites through interviews with the local community and dendrochronology
