Distribution patterns were categorized into three types. Numbers of embryos categorized in each type are shown. ICM derivatives indicate the cell layers derived from inner cell mass such as embryo proper and extra-embryonic mesoderm. TE derivatives indicate extra-embryonic ectoderm such as trophoblast gaint cells and the cells of ectoplacental cone. The first type showed existence of labeled cells in both groups of cell layers, the second type showed distribution of labeled cells only in ICM origin, and the third type exclusively in TE derivatives. Out of the blue embryos in Table 2, those embryos recovered with extra-embryonic ectoderm that were morphologically normal were analyzed. Because we did not dissect out embryos with extra-embryonic ectoderm in early experiments, the numbers counted were less than the numbers shown in Table 2.