Reproductive organs of 3 unmated female hares and 4 mated ones, which were killed at 10 hr (1 hare), 12 hr (1 hare) and 15 hr (2 hares) after copulation, were investigated histologically with a light microscope to determine the process of follicular growth and the timing of reflex (induced) ovulation in Lepus brachyurus brachyurus. The vesicular follicles observed in the hare belong to the‘spider’type characteristic of the order Lagomorpha. After copulation, the vesicular follicles rapidly increased in size (the greatest length 1.0-1.3 mm) and became the mature follicles (1.5-2.5 mm) . Such follicular growth and maturation in the hare were similar to those of the domestic rabbit. Although an ovum just after extrusion of the first polar body was recognized in a mature follicle, the details of ovulated eggs remained unknown because of preparation failures. The time required for the hare to ovulate after copulation was between 12-15 hr, and it closely approximated to the times required for other genera (Oryctolagus and Sylvilagus) examined so far in the Leporidae.

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In 4 adult male Hokkaido brown bears (Uysus ayctos yesoensis) in captivity, serum testosterope levels gradually began to increase from February in the middle of the torpor period, attained to a peak in April (6.8 ng/ml) or May (5.6 ng) after arousal, and decreased rapidly to the baseline value (below 1.0 ng) in June at the middle of the mating season ; the low level lasted into January at the first half of the torpor period. The testis sizes in March to August (4.94±0.34 cm ; N= 17) were larger than those in September to February (4.23 ± 0.30 cm ; N =17) (p<0.001) . Active spermatogenesis was sustained from February to September in the 4 male captives and confirmed also in 14 adult male bears shot by hunters during the March-May period. Thus, it was revealed that the duration of active spermatogenesis was longer by -4 months than that of the high serum testosterone level, and that the male reproductivity (spermatogenesis) generally continued longer than did the female receptivity restricted to the mating season from early May to early July.

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The chromosomes of ten raccoon dogs from northern Honshu of Japan were examined by means of conventional and/or differential staining. The B chromo-somes were present in all of the specimens examined, showing marked intra-and interindividual variations in number. The modal number varied from individual to individual, and the intraindividual variation in diploid number was exclusively related to the number of B's, as confirmed by C-staining. Heterozygous Robertsonian fission of the pair No. 6 was detected in three of these ten specimens examined, one of which was a mosaic with non-fission and fission cell lineages, 2n=38+B's and 2n=39+B's. It was pointed out that the fission rearrangements of the Japanese raccoon dog were not necessarily specific to the central and southwest Honshu populations, but also detectable in the northern Honshu population, and the rearrangements from these localities including five cases reported so far were all heterozygous. The possible role of heterozygosity in the Japanese raccoon dog was briefly discussed.

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Spatial structure of the grey red-backed vole (Clethrionomys rufocanus bedfordiae) was investigated by using trapping and radiotelemetry methods between April and May 1987 in an enclosure (2.1 ha) in Hokkaido, northern Japan. The locations of home ranges and overlapping patterns of home ranges were not different between trapping and radiotracking. Eight (four pairs) of 15 females showed communal nesting. Three pairs of them had kin-relationship (mother-daughter or siblings) . Communal nesting had been dissolved before the females gave birth to young in two pairs. There were no differences in the pregnancy rate between communal nesting and solitary females, but more parturitions were observed (or estimated) in the communal nesting females. The prolonged association of a male and a female was observed, which had not been reported in this species.

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Three one-hectare grids (A, B, and C) were set in broad-leaved natural woods in the suburbs of Sapporo, Hokkaido and the role of arboreal habitat space for forest rodents was measured by means of the following manipulations of the habitat. Rodent populations were censused six times during five months from June to October, 1985; three species, Apodemus argenteus, A. speciosus ainu and Clethrionomys rufocanus bedfordiae were recorded from all the grids. After the census in June, all trees (>3 cm in DBH) in grid B were covered with a sheet of plastic film at the basal part to prevent rodents from using arboreal habitats. In grid C, oat grains were supplied after the census in June with a container fixed at the hight 150 cm on a tree near each trap site (100 containers in total) . Grid A was used as a control. By these manipulations, the following population trends were observed after July : In grid B the population of A, argenteus which is most scansorial in habit increased less, while terrestrial A, speciosus and C. rufocanus were most abundant in this grid. In grid C, on the other hand, only A. argenteus increased and maintained a high density level through October ; the other two species did not show distinct increases. These findings indicate that arboreal habitat and food resources are more important for A. argenteus than for the other two species.

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Nest use pattern of the Japanese wild boar Sus scrofa leucomystax was studied in the Ebino Height, southern Kyushu, Japan, from November 1979 through February 1983. Nest data were collected by field sign surveys, which were con ducted along the fixed routes of 33.4 km in length in the study area (475 ha) . During the study period, 153 nests were divided into two types; one was a bower, a mound-like nest in which the wild boar sheltered, and the other was a bed, a nest without a roof. The wild boars built bowers more frequently than beds in all sea sons, probably due to cold temperature and much rainfall in the Ebino Height. The roof of the bower provides wild boars both thermal insulator and shelter from the wind and rain. Thickets of Miscanthus sinensis distributed widely as the under growth in the study area and provided suitable bower materials. Nest size de pended on the number of individuals resting in a nest and changed seasonally, prob ably due to seasonal changes of their social grouping pattern.

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