Some characteristics of the prostatic ACP of the rat were examined in the crude extract of each ventral and dorsal lobe using p-nitrophenyl phosphate (p-NPP) 2Na as the substrate. The Km was 1.24mM in both lobes and the optimum pH was 4.8. The optimum conditions for the measurement of the enzyme activity were more than 124mM for the substrate concentration, pH 4.8, 1-4mg/ml homogenate and within 30 min for the reaction. One hundred and thirty mM of p-NPP 2Na was ap-plicable since there were negligible spontaneous hydrolysis and no inhibition of the enzyme at this concentration. The comparison of the ACP activities at 5.5mM substrate concentration, which is widely accepted for clinical purpose, and at 130mM, which is equivalent to the concentration of more than 100 times of the Km, revealed that the enzyme activity might be underestimated in case of 5.5mM.
This method was applied to detect the changes of the rat prostatic ACP activity in the ventral and dorsal lobes with age. The activity was relatively low at immature stage and increased with age in both lobes. Weekly increment and tissue levels of the ACP activity showed a peak at puberty, i.e., 6-9 weeks of age, which coincided with a peak of the prostatic weight increment. Peaks of the incre-ment of the weight and enzyme activity, and the tissue levels of the ACP appeared a little later in the dorsal lobe than in the ventral one.
These results clearly indicate that the ACP activity in the ventral and dorsal prostate of the rat culminates at puberty as seen in other species, suggesting a positive correlation to increased tissue levels of androgens.

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Using a closed colony of Wistar-Imamichi rats, 10, 200 females were impregnated with 214 males. One of the sires was found to repeatedly cause small litter size deliveries. Another male with this characteristics was obtained by backcrossing of his daughter to the original male. Thereafter sib-mating was maintained. In the first and the second generations of sib-mating, 3 males out of 5 and 4 males out of 5 showed this characteristics. These animals were designated as small litter-line males and compared with randomly bred males (control males).
The litter size of small litter-line males was 5.4±3.7 (mean±SD), while that of the control males was 12.4±3.8. The number of implantation sites (6.7±2.9) was significantly smaller than that in the control (14.7±2.0). Fertility of the ova (46.2%) was lower than that in the control (96.9%). His-topathological lesions were observed in the testes and accessory reproductive organs in the small lit-ter-line males. Hypospermatogenesis was evident.
These findings indicate that the litter size of a rat is regulated by the sire. Hypospermatogenesis, possibly a genetic abnormality in small litter-line males, would decrease the number of fertilized ova and consequently, the number of implantations.

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The PGE₁, PGE₂ and PGF_2α were used as the substrates to histochemically demonstrate the activ-ities of prostaglandin dehydrogenases (PGDHs) in intact mouse blastocysts on Day 4 of pregnancy, in delayed implanting blastocysts on Day 10 and those on Day 10 but 18h after the administration of estradiol benzoate. Diformazan granules were deposited by the treatment with NISSEN and ANDERSEN method in the cytoplasm of both trophoblast cells and inner-cell-mass cells of the blastocysts when there was some activity of PGDH present in them. All of the activities of PGDHs in intact blasto-cysts were weak both in the trophoblasts and inner cell masses with the use of any kinds of sub-strates. However, all of the activities of PGDHs in the delayed implanting blastocysts either with or without the administration of estradiol benzoate were strong in the trophoblasts, but negative in the inner cell masses. Considering the present results as well as those on the metabolism of lipids and steroids in delayed implanting mouse blastocysts, the activities of PGDHs in such blastocysts seemed to be concerned with the metabolism of lipids and steroids.

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Bull and boar spermatozoa suspended in Ringer-fructose solution supplemented with 0, 1, 10 and 1000ng/ml of PGF_2α were incubated for 3 h at 37C and the effects of PGF_2α on the motility and the metabolism of spermatozoa were examined. No significant effects of PGF_2α were observed on the motility, oxygen consumption, fructose utilization and lactic acid accumulation in both bull and boar spermatozoa.

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Ovaries of ten neonatal doe fawns (2 to 40 days old), five yearling does (6 to 20 months old) and twenty-four adult does (2 to 20 years old) were used to investigate the postnatal development and seasonal and ageing changes.
1. Ovaries of neonatal doe fawns were filled predominantly with primordial and primary follicles and the largest follicle found in this group was about 0.5mm in diameter. Exceptionally large fol-licles exceeding 1mm were found in two doe fawns.
2. In ovaries of yearling does, particularly those obtained in a rutting season, more or less deve-loped follicles were noted. As no corpus luteum was found in a yearling doe group, it may be as-sumed that the follicle, though it attains 3 to 4mm in size, will not be ovulated. Various kinds of atretic bodies were commonly noted in neonatal and yearling doe groups.
3. The ovary weight of adult does showed a variation relating to the ovarian structure and the disappearance of the vesicular follicle was characteristic in aged does (more than 15 years old). Pri-mordial and primary follicles were also decreased in number in aged does. Therefore, the effective reproductive life span of the Japanese deer seems to be around 14 years.
4. Several large follicles attaining 4 to 5mm in size were noted in ovaries of adult does irrespec-tive of the season. A follicle which attained more than 5mm in size seems to be ovulated twice or three times during a rutting season (from October to December). In most ovaries of adult does, various kinds of atretic follicles were noted throughout the year.

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Morphological changes in the epithelium and smear from the vaginal vestibulum of cows were examined histologically at different stages of the estrous cycle and at 5 months of pregnancy using light and scanning electron microscopes.
A stratified cubic epithelium was observed during the estrous cycle and a stratified squamous epithelium during pregnancy. The epithelium was thickest at estrus and thinnest at pregnancy. Dur-ing the estrous cycle and gestation period many leucocytes were observed in the epithelium. Thenumber of leucocytes was greatest at estrous stages and their nuclei were elongated in the intercel-lular spaces.
In vaginal smears, the number of epithelial cells and leucocytes was the greatest at the estrous stages and decreased at diestrus, followed by a slight increase at around 13 days after estrus. All of the leucocytes were identified as neutrophils. The shape of the nuclei became string- and spindle-like in appearance. These nuclei migrated and gathered to form rope-like structures. Leucocytes ap-peared with epithelial cells in smears. The deformed nuclei appeared with neutrophils and when nuclear deformation of leucocytes occurred, there was a decrease in leucocyte number in the lumen of the vaginal vestibulum.

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Semen and its sperm rich fraction was collected from two Landrace and one Landrace-Large White crossbred boars (1 to 2 years old) one hour after injection of 12mg PGF_2α into rump muscles. The PGF_2α treatment improved libido to some extent and caused earlier erection of the penis in one boar. The duration of ejaculation, volume of semen and the total number of sperm in the sperm rich fraction increased following the injection by 32, 28 and 44%, respectively (P<0.01). The concentration and total number of sperm in the whole ejaculates increased by 23 (P<0.05) and 34% (P<0.01), respectively. No significant difference was seen in the viability of sperm in the sperm rich fraction stored at 15 C between the PGF_2α injection group and the control group.
These results suggest that the main effect of PGF_2α was the increase of the volume and total number of sperm in the sperm rich fraction and that those sperm rich fraction could be used for artificial insemination.

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Using the halved morulae of rats and mice obtained with microsurgical technique, the following items were investigated:
1) Production of aggregate embryos by the method of MINTZ¹⁾ and investigation on the subsequent development.
2) Observation on aggregation and fusion of the paired demi-embryos by scanning elec-trone microscopy (SEM).
3) Fluorescent vital staining (FITC & TRIT) of the paired demi-embryos and investga-tion on distribution of the dyes during development in the aggregate embryo in vitro.
Out of 107 pairs of rat's demi-embryos, 87 were successfully aggregated, of which 63 (58%) developed to the blastocyst stage. While, 85 out of 127 pairs of mouse demi-embryos suc-cessfully aggregated, of which 71 (56%) developed to late morulae and 14 (11%) to blasto-cysts. These rat and mouse aggregate blastocysts were slightly small in size but were found to have inner cell masses.
The observation by SEM revealed that the fused embryo at late morula stage had the structure of a linear sulcus running around the equatorial surface. The location of this sulcus seemed to be the border where the paired demi-embryos made contact to fuse each other.
The distribution of the fluorescent dyes showed that two hemispherical cell masses with different colors made contact at the central plane of the morula, and that in the blastocyst the inner cell mass was also consisted of two cell populations with different colors confront-ing either vertically or horizontally.
These observations suggested that two groups of cell mass might seldom mingle each other in the aggregate embryo during early developmental period until the blastocyst stage, thereafter two groups of blastomeres of different origin seem to begin mixing.

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An automatic embryo collector was devised.
The average number of embryos collected from ten superovulated cows, was 9.7 per head. Ex-cept two cases of failure, the average recovery rate was 80.0%.
The instrument may be useful in protecting the embryos from sudden changes in temperature.

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