In our laboratory we had been breeding the Japanese mouse, Mus molossinus Temminck and Schlegel since 1955. During the period, basing on 294 embryos and fetuses of 60 litters, the prenatal growth of several parts of the body, i.e. body weight, and neck-rump or crown-rump length, length of tail and hind foot, and also size of gonad and length of uterine horns are observed on all ages from 8 days to 20 days after copulation. The procedure in obtaining the embryos and fetuses was essentially the same as that described by MacDowell et al. (1927) and Enzmann (1935). The results are as follows : The growth rate of embryos and fetuses of the Japanese mouse is relatively slight during the early days preceding implantation. After implantation a rapid and marked increase in weight occurs. The average weight of embryos between 8 days and 9 days after copulation is 0.72±0.020 mg, between 19 days to 20 days in female fetuses 1026.88±24.581 mg, and in male ones 1121.33±31.033 mg. The average neck-rump length of embryos between 8 days and 9 days after copulation is 1.27±0.018 mm, crown-rump length between 19 days to 20 days in female fetuses 24.69±0.138 mm, and in male ones 24.87±0.146 mm. The average length of tail of fetuses between 11 days and 12 days after copulation is 4.00±0.000 mm, between 19 days to 20 days in female fetuses 9.09±0.097 mm, and in male ones 9.57±0.098 mm. The tail coefficient of the early embryos is relatively greater than that of other ones. The average length of hind foot of fetuses between 11 days and 12 days after copulation is 1.50±0.000 mm, between 19 days to 20 days in both sexes 5.00±0.000 mm. The growth curves representing these weight and length increases are typically sigmoid with the inflection point on body weight, and neck-rump and crown-rump length, and length of tail between 15 days to 16 days after copulation. The inflection point on hind foot is between 17 days to 18 days after copulation. It seems that there is little difference between female and male fetuses. The average size of left ovaries of fetuses between 15 days and 16 days after copulation is 0.77±0.009×0.400±0.000 mm, and that of left testes is 0.85±0.009×0.680±0.007 mm. That of left ovaries between 19 days to 20 days after copulation is 0.50±0.000×0.50±0.000 mm, and that of left testes is 1.00±0.000×0.95±0.011 mm. The average length of each uterine hornes of fetuses between 15 days and 16 days after copulation is 1.60±0.034 mm, and that of fetuses between 19 days to 20 days 4.00±0.000 mm. The each length of both uterine hornes is just same.
Mendeley出力
