イエコウモリ

In the previous paper(Hiraiwa and Uchida,'55) we experimentally studied that the spermatozoa introduced into the uterus of the bat, PiPistrellus abramus abramus(Temminck) in the autumn are able to retain their fertilizing capacity for 118 days and fertilize the ova which have been discharged from the ovary in the spring. In this case, how are the spermatozoa stored in the uterus? Looking over the literatures one notes that most former workers generally believed that the spermatozoa stored in the bat uterus in the winter are in a very active state. We have some doubts, however, whether the semen stored in the uterus during such a long period retain similar conditions in their properties such as the viscosity of semen, percentage and index of motile sperm, and sperm concentration. On the otherhand, winter and spring copulations have been observed in the cave-dwelling bat Myoiis, though not noticed in Pipistrellus except the ordinary autumnal copulations. If winter or sprlng copulations occur also in some individuals of the bat, large difference may exist between the properties of semen stored in the uterus since autumn and that introduced into the uterus by the later supplementary copulations. Accordingly if there is a great disparity in the properties of semen, we may be able to admit that copulations occur again in the winter or spring. In order to solve these two problems above mentioned, studies on the properties of semen were made quantitatively. The results may be summarized as follows: 1. The stored semen are classified into three types by their properties. The semen contained in the uterus of bats captured in the autumn belong to only the first type(Fig. 2), but the semen in the spring consist of the first, second and third types(Figs. 3, 4 and 5), and large differences in properties exist among three types(Tables 2 and 3). And the index of motile sperm is shown in inverse proportion to the sperm concentration of semen(Fig. 1). Although our results disagree with those of previous workers and Wimsatt's observations('42, '44,), it is obvious that the spermatozoa found in the uterus in the spring are not always in a active state, because in about half individuals the majority of spermatozoa lose their activity, very few being surviving. 2. Judging from the histological observations, the large difference in the properties of stored semen has never been based on the endogenous factor, i.e., the influence of estrous or preovulatory conditions of female genital organs. It is, accordingly, believed that the exogenous factor, i.e., the disparity in length of passage of days after copulations gives rise to such a large difference in the properties of semen. In the spring, On the other hand, the existence of such abundant active spermatozoa as are found in the first type semen introduced into the uterus is never found anywhere except the cauda epididymis of male bat. In conclusion, then, it appears that the supplementary copulations take place at relatively high percentages in the winter or spring. 3. In the third type semen, the spermatozoa shown histologically with their heads towards the uterine. epithelium(Fig. 7), corresponds to the motile sperm seen by direct observations. 4. The third type semen, together with the first and second type semen, may be capable of fertilizing the ova, and even a small volume of semen(+) is enough for fertilization(Table 1)