飼育下におけるハタネズミの成長と発育

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Growth and development of 69 young in 15 litters of Microtus montebelli montebelli were studied in the laboratory for a period of 40 weeks after birth. Newly born young was reddish pink and possessed mystacial vibrissae and fine bristles on the lips and chin. The dorsum was throughly covered with hairs by day 4 and juvenile pelage nearly completed by day 11. The lower and upper incisors erupted through the gums at an average age of 4.8 days (4-6) and 5.3 days (4-9), respectively. Meatus opened between 6 and 9 days of age (mean 7.1) . Opening of the eyes occured from the sixth to ninth day of age, with a mean of 7.9 days. The digits were separated at the mean age of 7.1 days (7-8) in hand and 8.4 days (7-9) in foot. The young began to eat solid food by day 9, but nursing continued to days 14 or 18. Growth in total length, head and body length, tail length and ear length was most rapid in the first 3 weeks. Length of hind foot increased rapidly in the first 2 weeks and the growth of it essentialy completed by the fifth week in females and by the eighth week in males. From the fifth week, the mean values of weight, total length, head and body length and tail length of females were significantly (P≤0.05) less than those of males. From the fourth week, the mean values of hind foot length in females were significantly (P≤0.05) less than those of males. Sexual differences were not evident in length of ear and tail per cent.
日本哺乳類学会の論文