Three distinct mammal communities were recognized in a forest region on the western slope of Mt. Fuji, Honshu, Japan. Among them, the subalpine conifer forest community is relatively poor both in the number of species and in the density of populations of small mammals and is distinguished from the subalpine deciduous forest community by the absence of Apodemus speciosus speciosus and rarity of Eothenomys kageus. The low mountain mixed forest community is characterized by the presence of Urotrichus talpoides hondonis and the absence of Dymecodon pilirostris.
In the most of species found in this region, the habitat range seems to clearly correlate with the nature of forests. However, those of Dymecodon and Urotrichus are exception and seem to be mainly determined by a kind of competition between them.
In the region above Shôjiguchi Ni-gôme, 1, 500-2, 380 m alt., the habitat range of Dymecodon was completely confined to an area above and that of Urotrichus mostly to an area below a line at about 1, 600 m alt. in a mixed forest. However, two specimens of Urotrichus were obtained in the habitat range of Dymecodon, one at 2, 380 m and the other at 1, 670 m alt. This indicates that the habitat ranges of these two species are mostly segregated, but the territory of Dymecodon population is not so exclusive as that of Urotrichus and contains several individuals of the latter. Quite same phenomena of such special segregation between these two species have been known from Mt. Hayachine, Tohoku District, and Mt. Yatsugatake, Central Honshu.
This can be explained clearly by a following hypothesis. There is a “competition by power” between those two shrew-mole species which are nearly related and similar in general habits including the ecological niche but are slightly different in size and physical strength. So that the individuals of the stronger species, Urotrichus, able to successfully maintain their territories against the individuals of the weaker one, Dymecodon, but the reverse is not true. If the population density of the stronger species is nearly in saturation in an area, then the individuals of the weaker species may be completely driven out from there. But, the stronger species probably able to invade rather freely into the range of weaker species and to live on there.
It is probable that Dymecodon, evidently more primitive and older in origin than Urotrichus, had probably covered nearly completely the foot of Mt. Fuji in ancient times. After that Urotrichus had arrived there and gradually drove out Dymecodon from the foot to subalpine region. However in some regions where Urotrichus perhaps had failed to invade by some kinds of barriers, populations of Dymecodon have been maintained well to the present day. A population of Dymecodon at Lake Motosu region, 910m alt., may be such living remnant.

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A study of reproductive activity in the Japanese long-tailed field mouse, Apodemus argenteus, was carried out from March 1960 through November 1961 at the deciduous forest in Moiwa-yama, Sapporo. During the study, 527 field mice were trapped and grouped into overwintered or current year's individuals by degree of tooth wear.
In the population studied, reproductively active males (with tubular epididymus and swollen seminal vesicles) and females (with turgid uteri or embryos) were found at the same time from April to September in 1960 and from March to August in 1961. The majority of reproductively active mice were overwintered ones through the breeding season. Although a small part of young adults with an estimated age of over 2 months after birth was capable of reproducing during their first summer of life, a lower level of reproductive activity was found in the young adults than overwintered ones. Average litter size for the overwintered females was 4.1, while that for the current year's ones was 3.2.
Young mice appeared first in the population during May or June and comprised a low percentage of the population until July or August. In later part of the breeding season, the percentage of immature individuals increased so that the percentage of reproductively active individuals in the population showed a rapid decrease. There were no significant monthly changes in sex ratio, although there was a bias toward males in the overwintered population in 1960.
The average body weight for overwintered mice was about 13 g in the spring and rose abruptly to about 17 g by the summer. Young mice born at the beginning of the breeding season reached sexual maturity and approached weight of overwintered ones, while young born in the second half of this period weighed an average of about 10g through the summer.

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Reproductive data were obtained from dissection of 417 Japanese shrew moles, Urotrichus talpoides hondonis THOMAS, 1908, collected from population in Yukyuzan park, Nagaoka city, Niigata pref., central Honshu, Japan from November 1966 through October 1967.
The principal breeding season extends from late February to May ; during this period, double litters occur in some Japanese shrew moles (10 to 20 per cent of adult females) . There is some sporadic breeding activity in June and July. The second small breeding peak may occur in late August or September. The mean litter size in utero and the 95 per cent fiducial interval is 3.75±0.44. Dispersal of young from parental nest begins in late April and May. There is a small amount of dispersal of young in October and early November. There is no indication that the young males and females breed during their first calendar year of life.

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In this paper, the authors recorded the embryo-size in five species of Japanese native bats. The results are shown in following table. Moreover, in June 23rd, 1965, we obtained in Nagano City 6 specimens of lactating females of Myotis macrodactylus that were hanging with 1 baby under each breast.

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