Abstract
Young (3β5 months of age) and senescent (12β17 months of age depending on the species) female mice, hamsters and rats were mated with young mature males and examined for numbers of degenerating ova. Young female mice, hamsters, rats and senescent rats exhibited normal numbers of ova following ovulation and, in general, normal numbers of blastocysts before implantation. In contrast, on the morning of ovulation some senescent mice and hamsters exhibited degenerating ova in the isthmus or isthmicβuteroβtubal region of the oviduct, while normal ova were found in the ampulla. Degenerating ova were also located in the uterine horns of one mouse and hamster before implantation (day 3 of pregnancy). Another hamster at the same stage of pregnancy exhibited 24 degenerating ova and nine blastocysts, all of which remained in the oviducts except for one blastocyst recovered from the uterus. In a previous study (Parkening and Soderwall, '75), a histological examination of the number of corpora lutea from ovaries removed from senescent female hamsters whose oviducts contained large numbers of degenerating ova indicated the deteriorating ova were not ovulated following mating. Why ova from the previous unmated estrous cycle(s) remain in the oviducts of some senescent mice and hamsters remains to be determined.