41.   Normally, doctors start by giving women fertility drugs to stimulate their ovaries to produce more eggs than usual.

42.   Others, including many of the larger species, are ovoviviparous, meaning that the female produces eggs that hatch within her.

43.   One mouse that produced an egg, produced a second the following month from the same fragment of ovarian tissue.

44.   Such stem cells, he said, could be used only in the women who had produced the eggs.

45.   They produce two eggs a year.