BINUCLEATE AND TRINUCLEATE OOCYTES IN POST-OVULATION OVARIES OF RANA PIPIENS

¹ Division of Biology, University of Pennsylvania, Philadelphia 4, Penna.

1. Fifty-six binucleated and two trinucleated cells were found among 249,616 young transparent primary oocytes in post-ovulation ovaries of 25 females of Rana pipiens (0.022%).

2. Multinucleated oocytes were absent in 15 females, present in 10. Eight of these 10 produced only one to four binucleates each: one female was the source of 1 tri- and 14 binucleates; and another gave the remarkable number of 24 (0.175%), all binucleates.

3. The multiple nucleated condition did not seem to be correlated in any way with the size of the female, the abundance of her eggs, nor the size of the egg.

4. In none of the binucleates did the volume of either of the two nuclei approach that of the nucleus of a mononucleate of the same size. The one exception was egg #43 where one nucleus did have exactly the volume of the control, the other about half that.

In 29 of the 31 measurable binucleates the two nuclei were of approximately the same size and the sum of the two volumes equalled that of the mononucleate, except in one case where it was half.

The origin of binucleate oocytes remains uncertain; it may be connected with a final division of an oogonial nucleus that was not followed by cell division. In this case the two nuclei would both be diploid.

5. The two trinucleates conformed in general to the same pattern as the binucleates as to their distribution, size of oocyte, and the volumes of their nuclei. The sum of the three nuclear volumes approximated that of the mononucleate.

6. In two cases where the nuclei were markedly unequal in size, there was a definite difference in the appearance of their chromatic granules. These bodies were more abundant and finer in the larger nuclei, peripheral, larger and more distinct in the smaller nucleus.