It was observed with vaginal smears that the 4-day cyclic mice (IV CS strain) show a 3-day estrous cycle in various conditions: after the weaning (maters), after the pseudopregnancy, in the proximity of males and after the progesterone-treatment (0.5 mg/a/day, for 10 days).
Mice were housed in artificially illuminated (lights on 5 am to 7 pm) animal room.
The results obtained are as follows.
1) The typical vaginal smears checked in the day time on the 3-day estrous cycle showed stages of proestrus, metestrus and diestrus as follows; on the first day (Proestrus): nucleated epithelial cells and cornified cells (PLATE 1); on the second day (Metestrus): many leucocytes, nucleated epithelial cells and thick mucous verge (PLATE 2); on the third day (Diestrus): few nucleated epithelial cells, cornified cells and leucocytes (PLATE 3).
2) The appearance rate of the 3-day estrous cycle were 80-90%, 80%, 60%, 10-30% and 90% in the case after the weaning (the 21th day weaning, litter size: 8), after the progesterone-treatment, after the pseudopregnancy in the proximity of males for 24 hrs. and in continuous proximity respectively (Table 1 and 2).
3) In the cases after the weaning, the pseudopregnancy and progesterone-treatment, 3-day estrous cycles occured following a 4-day estrous cycle and repeated 16 cycles and then returned to 4-day estrous cycles (Fig. 1).
4) Three-day estrous cycles were repeated continuously average 5.6, 5.5, 3.8, 1.4 and 7.8 cycles in the case after the 21th day weaning, after the pseudopregnancy, after the progesterone-treatment, in the proximity of males for 24 hrs. and in continuous proximity of males (Table 3).
5) In the 3-day cyclic mice living with male mice separated by wire-netting, spontaneous ovulation was observed at 14 am on the day of proestrous stage (Table 4, Fig. 2).
6) While mating was observed on the night of the day of proestrous stage in the 4-day cyclic mice, mating in the 3-day cyclic mice was on the night of the day of diestrous stage.

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Effect of estradiol pretreatment on induction of ovulation by progesterone treatment is observed in the 4-day cyclic mice (IVCS strain) and rats (Wistar-Imamichi strain) under the constant lighting from 5 am to 7 pm.
1) In the 4-day cyclic mice, pre-treatment of estradiol (0.01 pg/mouse) at 10 pm on the day of metestrous stage followed by progesterone injection (0.031-0.100 mg/mouse) at 7 pm on the expected day of diestrous stage, caused an increase of ovulation rate induced on the next day (the expected day of proestrous stage) compared with the case by single injection of progesterone (Table 1, Fig. 1).
2) Treatment in a similar manner on the 4-day cyclic rats, (estradiol 10 μg and 40 μg/rat, at 5 am 1 pm; progesterone 3 mg/rat, at 8 am 1 pm) caused an increased ovulation on the same day, while ovulation rate is less than the case of mice (Table 2, Fig. 2 and 3).

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Effects of load on the motility of uterus during estrous cycle have been studied with excised uteri of rats by the method of Magnus. The rats were killed by decapitation and uteri were taken immediately. The both ends of the uterus which was cutt from vagina and ostium uterinum, and was separated from ligamentum uteri thereafter, were tied to the apparatus of Magnus in Ringer solution at 38 ± 0.5°. Then, the excised uteri were examined under the conditions of the load with two, three, four, five, six and seven times' weight, respectively.
The observation of the spontaneous motility of the excised uteri was commenced regularly from 30 minutes after the stabilization in Magnus apparatus.
The results were as follows :
1. When the utreri during estrous cycle were loaded with two and three times' weight among 6 sections as described, the uterine motility was very weak and irregular.
2. In the cases loaded with 4 and 5 times' weight, the characteristic uterine motility that was stabilized tonus and contraction of uterus, was observed in each stage of estrous cycle.
3. The motility of uterus in proestrus stage was comparatively large; small contraction in relaxation phase and soon after, large one appeared alternately. The frequency of small and large contractions were observed about six times in ten minutes respectively.
4. In estrus stage, the largest uterine motility was observed ; the contraction of uterus was rhythmical. And the frequency of the contraction was about five and six in ten minutes.
5. In metoestrus stage, the motility of uterus was relatively weak; small contraction curves were observed in contractive phase. The frequency was about six in ten minutes.
6. The contraction curve of uterus in diestrus stage was weak and irregular.

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Thirty-one kids of Saanen and Japanese native breed, ranging in age 2 to 15 weeks, were treated with gonadotrophins, PMS and HCG, to induce superovulation. They were inseminated artificially in the uterus with semen from fertile hegoats every 24 hr during oestrus following superovulatory treatments. Ova recovery was performed in vivo or in vitro 3 to 5 days after the HCG injection. Sixteen fertilized ova, which were collected from kids, were transferred surgically to the uterine horn of seven recipients which were adult Saanen goats and synchronized within ± 2 days in oestrus with the donors. The results obtained were as follows.
1) A total of 619 ovulations occurred in twenty-nine of thirty-one treated kids which were 5 to 15 weeks in age. It will be noted that there was a marked increase in number of ovulation points in the ovaries of treated kids which were more than 7 weeks in age.
2) A total of 256 ova was recovered from twenty-four kids except five cases. Only 53 ova from nine kids have been fertilized.
3) Three of seven recipients became pregnant following the ova transfer, and produced five kids, a single or twins per a pregnant recipient, normally.

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Sex ratios in rats were studied among 12, 492 animals of the Wistar-Imamichi strain which were born at Dr. Imamichi's Laboratory of the Nippon Veterinary and Zootechical College in 1969 and 1970. Analysis on sex ratio was performed by the same method as described in a previous report and used to determine swine sex ratio³⁾. The classes which showed a shift of sex ratio to either sex were cited mainly in tables. The results obtained are summarized as follows.
Total sex ratio (Table 1): In a total, the sex ratio was 49.2%. It cannot be said that three was any significant shift of sex ratio to either sex even at 5% level.
Paternal or maternal individuals (Table 2): Of the paternal individuals obserbed, only three individuals gave rise to a shift of sex ratio to female in their offspring.
All the maternal ones obserbed, however, showed a shift of sex ratio to either sex.
Litter series (Table 3): A shift of sex ratio to female (significant at 5% level) was seen in one class (litter series 2). When the litter series were grouped, however, no shift of sex ratio was noticed at all.
Litter size (Table 4): In one class (litter size 7), a shift of sex ratio to female (significant at 1% level) was recognized. When the classes of litter size were grouped, however, no such shift was seen at all.
Season (Table 5): Both secondary and primary sex ratios in winter were significantly low at 1% level. When analyzed annually, sex ratio was significantly low at 1% level. When analyzed annually, sex ratio was significantly low in the winter of 19691970 (from December, 1969, to February, 1970). There was a significant difference in secondary sex ratio between winter and any other season, and one in primary sex ratio between winter and spring, and winter and summer.
Age of parents (Table 6): No shift of sex ratio was seen in any group of paternal or maternal age, or any group of age. A significantly low sex ratio, however, was observed in one age group (one month superior in peternal age to maternal one).
Annual sex ratio (Table 7): No annual shift of sex ratio was noticed during two years in the present study.

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[in Japanese]

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