11.   The Advanced Cell Technology cloned human embryos grew for a few hours, long enough to form clumps of six cells, according to the company.

12.   The cow embryos grew in the surrogate mothers for five to six weeks, with the stem cells changing into useful tissues.

13.   Then scientists must buck the odds in getting the embryos to grow and isolating stem cells from them.

14.   When the embryo had grown in the laboratory for several days and appeared healthy, the researchers transferred it to a surrogate mother cow.

15.   However, it was an ectopic pregnancy, in which the embryo grows outside the womb in the fallopian tube.

16.   In some cases embryos grow abnormally large, Jaenisch said.

17.   Now, he said, the frog experiment has verified that embryos can grow normally also.

18.   They then implanted the cloned embryo into a surrogate cow and let the embryo grow for about six weeks before removing it.