The recent discussion of Hartman ('26), regarding polynuclear ova and polyovular follicles, emphasizes the common occurrence of such follicles and ova in the majority of animals on which reports have been made. Hartman's thorough review of the extensive literature makes it necessary to refer only to those papers which apply directly to this study. There is only a single report-Chappellier ('09)-regarding non-atretic polyovular follicles, and one (Blanc, quoted by Hartman) mentioning a polynuclear ovum, in the mouse. Kingery ('14) mentions polynuclear ova, but it is clear that he regarded these as being atretic. The data presented here are the result of a study of one hundred ovaries of the mouse, representing sixty-four adult animals, a single ovary having been removed from one group. The collection of these data on the occurrence of polynuclear ova and polyovular follicles was incidental to a study of follicular atresia (Engle,'27).

Polyovular follicles are not so abundant in the mouse as they are in the opossum. They were found in only twelve ovaries in the series of one hundred of the former, while Hartman reported one or more such follicles in all but twelve of 150 of the latter. A polynuclear ovum was found but twice in this series. It is necessary to exclude atretic ova with fragmented nuclei, which often give the appearance of a polynuclear condition, but which are secondary in origin and not true polynuclears. These two polynuclear ova, one with two and one with three nuclei, were clearly not the result of atresia.