title: Anomalous litters in hybrid mice and the retention of spermatozoa in the female tract.
abstract: Suspected superfetation was investigated in a Glasgow hybrid stock of mice. The male was removed either (i) a few days before parturition, or (ii) immediately after mating and on 23 and 25 occasions, respectively, a second litter was born. Members of the anomalous litters were inbred for 10 generations, but the incidence of supernumerary litters did not increase beyond 2-5%. The anterior part of over 500 reproductive tracts, at various stages of pregnancy and after parturition, were serially sectioned but a second set of embryos was not found. The second gestation was of normal length and superfetation was not therefore considered to be the cause of the anomalous litters. In two females, one non-pregnant and one pregnant, spermatozoa were found in the uterus and oviducts 8 days after mating and in distended uterine glands 15 days after mating respectively. It is concluded that the anomalous litters were derived from the fertilization of eggs ovulated at the post-partum oestrus by spermatozoa which had been retained in the female tract for at least 23 days.
mesh_terms: D000818:Animals; D001947:Breeding; D005187:Fallopian Tubes / Q000033:anatomy & histology; D005260:Female; D007774:Lactation; D008098:Litter Size; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010053:Ovary / Q000033:anatomy & histology; D011247:Pregnancy; D013094:Spermatozoa; D013476:Superfetation; D013997:Time Factors; D014599:Uterus / Q000033:anatomy & histology