Of the remaining females from Harding County, three collected on May 29 had enlarged uteri, whereas two collected in late June evidenced no gross reproductive activity.
"Mammals of Northwestern South Dakota"
Kenneth W. Andersen
It has been shown that the os uteri is not closed, as was once supposed, immediately on conception.
"Aids to Forensic Medicine and Toxicology"
W. G. Aitchison Robertson
Of the five females which he mentions, the first three, one with unfertilised ova in the uteri, two five and six days after heat, could not have been pregnant, but the other two killed eighteen and twenty-one days after heat might, since pregnancy lasts only eight days, have been pregnant, the young having died at parturition or before.
"Hormones and Heredity"
J. T. Cunningham