Search for: [Description = "Earliest evidence of vaginal perforation in both field and laboratory Microtus towsendii towsendii \(Bachman, 1839\) in the spring\-summer season occurs at the body weight of 15\-19 g. Virtually all field females are perforate in 25\-45 g weight cathegory, but laboratory females tend to be somewhat heavier before vaginal introitus takes place and first estrus may not occur until several weeks thereafter. Sterile cycles were not perceived in females that were approaching puberty\; rather, the interval between vaginal performation and first estrus was characterized by dietrous smear."]

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