ハツカネズミ

The collection of the Japanese mice, Mus molossinus Temminck and Schlegel, were made from June, 1955 to April, 1960 in Fukuoka district. I have observed about the external characters of the adult mice, such as body weight, length of head and body, tail, hind foot and ear, frequency distribution of variety in belly colour phase ; and the skull, namely, length of basilar (X), palatilar (Y), diastema (i-m_1), foramen incisivium, m_1-m_3, m_1-m_1, and nasals ; and also the reproductive organs, i.e. size and weight of ovaries, uteri, testes, epididymides, vesicular and coagulating glands. The results are as follows : 1. The average body weight of adult female mice is 12.44±0.121 g ; and that of males 12.63±0.101 g. The average head and body length of females is 72.25±0.406 mm ; and that of males 73.77±0.300 mm. The average tail length of female mice is 60.71±0.369 mm ; and that of males 62.24±0.318 mm. The tail coefficient is 0.84 in both sexes. The average hind foot length of female mice is 15.01±0.09 mm ; and that of males 15.92±0.009 mm. The average ear length of female mice is 11.62±0.012 mm ; and that of males 11.88±0.014 mm (Table 1). 2. The growth of hind foot and ear seems to stop before the mice reach to sexual maturity, though body weight, and head and body length continue to grow for a while afterwards (Table 1 ). 3. The belly colour of Japanese mouse is divided into four groups, namely, gray, slaty, white and buffy groups. Percentage of gray is 6.9 in female and 7.9 in male; that of slaty 10.4 in female and 9.8 in male; white 77.2 in female and 75.9 in male; and buffy 5.5 in female and 6.4 in male. There seems to be a little seasonal variation of belly colour (Table 2 ). 4. Ages were assessed by the wearing degree on grinding surface of m_3. I divided adult mice into four groups by age, i.e. Stage 1 (The rather young adult period. The crown surface of m_3 begins to wear, but remains original pattern.), Stage 2 (The adult period. The crown surface of m_3 wears moderately.), Stage 3 (The more advanced adult period. The crown surface of m_3 wears conspicuously.) and Stage 4 (The senile period. The crown surface of m_3 wears out completely, and dentine is surrounded by a single enamel-ring.). However, there is little conspicuous difference by the age constitution in size of various portions of the adult skull. In 117 adult mice (Females 62, Males 55), average length of basilar (X) is 16.8±0.074 mm in female and 16.4±0.077 mm in male ; that of palatilar (Y) is 8.8±0.044 in female and 8.5±0.050 in male ; that of X-Y is 8.0±0.056 mm in female and 7.8±0.052 mm in male ; that of diastema is 4.7±0.034 mm in female and 4.6±0.037 mm in male ; that of foramen incisivium is 4.3±0.023 mm in female and 4.2±0.034 mm in male ; that of m_1-m_3 is 3.1±0.019 mm in female and 3.0±0.012 mm in male ; that of m_1-m_1 is 3.0±0.015 mm in female and 2.9±0.013 mm in male ; and that of nasals is 6.8±0.045 mm in female and 6.5±0.039 mm in male. The skull grows anteriorily and posteriorily from the dead centre ; the posterior extension (X-Y) being greater than anterior extension (Table 3 ). 5. The average size of left ovary is 2.21±0.014　×　2.12±0.019 mm, the average total weight of both ovaries is 4.33±0.06 mg. The average length of left uterine horns is 23.83±0.352 mm; while that of right ones 26.92±0.351 mm. The average width of left uterine horns is 1.44±0.036 mm; and that of right ones 1.45±0.035 mm. The average total weight of both uterine horns is 35.35±1.252 mg (Table 4). The average length of right uterine horns is larger than that of left ones. 6. The average size of left testes is 6.43±0.041 × 4.51±0.008 mm, and the average total weight of testes is 74.92±1.205 mg. The average width of left caput epididymides is 2.32 ±0.007 mm, and the average width of left caudal epididymides is 2.35±0.008 mm. The average total weight of left ones is 16.26±0.217 mg (Table 5). 7. The average width in the widest portion of left vesicular glands is 3.18±0.042 mm. The average width of left coagulating glands is 2.03±0.032 mm. The average total weight of vesicular and coagulating glands is 64.3±1.213 mg (Table 6).