It has been often found that vertebral numbers of mice are varied among a few inbred strains as well as shapes of bones. This paper describes the distribution of vertebral numbers of inbred mice-strains dd, rr, ss, and C57BL, during 60 days after delivery to compare the mode of vertebral development among them.
1) Numbers of cervical and thoracal vertebrae were 7 and 13 respectively in all mice of 4 inbred strains regardless of ages.
2) In most of the cases lumbar vertebral numbers were 6 in dd, ss, and C57BL, but 5 in rr. Skeletal types of asymmetry, caused by the sacralization of the last lumbar vertebra either in the right or in the left side, was found more frequently in dd and rr than in the others, and to be the least in ss. These asymmetrical types were observed in higher frequency in the right side except the case of ss strain.
According to this sacralization of the lumbar vertebra, distribution of sacral vertebral types in each strain showed the same tendency as that of lumbar vertebral numbers. Sacral vertebral numbers, however, were mostly 4 or 3, and showed the similar manner of distribution in dd, rr, and C57BL, but not in ss strain.
3) Caudal vertebral numbers appeared to increase rapidly until 10 days following the delivery in each strain, thus attained to those of adult mice. But it took roughly 30 days until both shapes and numbers became same as adults'. As for the caudal vertebral numbers, there was no difference among the strains.
4) Variation of lumbar and sacral vertebral numbers was marked in each strain. This seems to be due to the reason that the lumbar region begins to develop later than the other regions, and the environment is ready to influence the development of vertebrae in that region at early embryonic stage.
5) Interfrontal bone was found most frequently in C57BL, and was less in decreasing order of rr, dd and ss. Mice having this bone are not considered to be abnormal in any pathological sense, because of their normal performance of growth and of reproduction.

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マウス, ラットの人工授精法について, 偽妊娠誘起法, 授精適期の判定, 精液の採取, 精液稀釈液, 精液注入法などの検討を行なったのち, マウス16例, ラット4例について人工授精を実施した。主な結果は次のものである。
1.稀釈液については, 生理的食塩水, ロック氏液, 糖燐曹液について検討したところ, マウス, ラットのいずれにおいても, ロック氏液が生理的食塩水, 糖燐曹液に比べて時間の経過に伴う精子の生存率, 活力の低下がゆるやかであり, 稀釈液として他の2つよりもすぐれていることが分った。
2.マウス16例, ラット4例について人工授精を行なった結果については, マウスのばあい, 注精時刻が9～12p.m.のものでは10例中4例が正常の子を分娩し, 1例は受胎したが妊娠15日目に流産した。注精時刻8p.m.以前のものでは6例中1例も分娩しなかった。ラットのばあい, 注精時刻9p.m.のものが1例正常の子を分娩した。
3.マウス, ラットの夜間における人工授精は自然条件における♀の交配適期の時刻に注精したばあいに成功率が高いのではないかと考えられる。

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