イエコウモリ

That bats copulate in autumn but fertilization occurs in spring of the ensuing year, has been studied by many investigators and become an established view. It has become known that in the bat Pipistrellus abramus abramus, too, mating takes place on and after the last decade of October, and ovulation and fertilization late in April (Uchida, '53). Whether or not the spermatozoa introduced into the uterus in the autumn are identical with the ones that fertilize the ova in the spring, however, has been undetermined. It has been repeatedly mentioned that the problem can be decisively solved only by capturing inseminated females in the autumn, keeping them isolated from males throughout the winter, and examining their genital tract in the spring to realize the consequent of fertilization or pregnancy. Since workers attempting to try this procedure meet with the difficulty of keeping bats throughout the period of hibernation, the experimental evidences for this problem have been yielded in only two genera of cave bats including three species, i.e. , Myotis sodalis (Gates, '36), Myotis lucifugus lucifugus (Gates, '36; Wimsatt, '44a) and Eptesicus fuscus fuscus (Folk, '40; Wimsatt, '42, '44a). Therefore, further confirmation for another genus of bats is desirable. In a previous paper (Hiraiwa and Uchida, '55a:), we have preliminarily offered an evidence for this problem in Pipistrellus. Since the paper has been written in Japanese without English summary, we describe the data in brief here. One female bat collected on November 30, 1953 (Bat A in table 1) was isolated from any male to March 23, 1954 under artificial hibernation. On March 24th the bat was awaked from hibernation, and 5 rabbit units of anterior pituitary hormone were given respectively on the 25th and 27th. The bat died on the 29th after 119 days in isolation. It was found that a discharged ovum was penetrated by sperm and the second maturation division was in the telophase just after extrusion of the second polar body (Figs. 1. 2 and 3), but fertilization in a narrow sence, i.e. conjugation of the female and male pronuclei, did not yet occur. The present experiments extend the same observation made in the former preliminary paper to a number of animals, to prove in Pipistrellus more concretely that the spermatozoa of the fall matings are capable of fertilizing and further developing the ova discharged from the ovaries in spring. Seven female bats collected in the late autumn and early winter of 1954 were put in to a refrigerated chamber where the bats remained during hibernation, being isolated from any male, to March 16, 1955. The bats were confined in 5" x 3" x 3" wood box which was placed in the refrigerated chamber where temperature of about 39°F. (4℃.) and humidity of about 80 % were constantly maintained. On March 17th the bats were awaked from artificial hibernation by being removed to a laboratory room. Although ovulation occurs late in April under natural conditions, in order to induce ovulation artificially and to find the results as early as possible before the bats die, the animals were injected hipodermically with 25-30 rabbit units of Hypohorin, anterior pituitary hormone. On March 17th were given 5 units (10 units in Bat No. 53) and each 10 units on the 21st and 26th, being dissolved in 0.5cc of Vitamin B1 solution. The bats were fed with the larvae of Tenebrio molitor (mealworms) after awaking from hibernation, but they became weakened gradually and died after various lengths of survival. The bats, of course, had been isolated from any male from the date collected of 1954 to the date of death of 1955 (isolation period in table 1). Their genital organs were fixed in Bouin's solution, sectioned serially at 6/2, stained in Heidenhain's iron hematoxylin and eosin, and examined under the microscope to ascertain that fertilization had taken place or not. Table 1 is the summary of the experimental data on eight animals including Bat A of preliminary paper. In Bat No. 76 (175 days in isolation) three segmenting ova were found in the tube and the ova consisted of approximately thirty-five cells each (Fig. 4). Bat No. 83 (159 days in isolation) possessed two ova in the two-cell stage in each tube (Figs. 5 and 6). In Bat No. 53, No. 84 and No. 86 isolated for 175, 144 and 146 days respectively, the female and male pronuclei were in close contact within the ova (Fig. 7), and in Bat No. 75 (160 days in isolation) both pronuclei conjugated. Bat No. 110 (134 days in isolation) possessed two ova in the four-cell stage in the tube (Fig. 8). It is difficult to determine the date of ovulation, although it is supposed to take place late in April under natural conditions. Therefore another purpose of hormone injection was to know the date of ovulation and fertilization. Judging from the examinations of the animals which were awaked and injected on the 17th of March and died at various intervals after the last injection, it was supposed that ovulation and fertilization occurred almost simultaneously on the 24th of March. Thus we could know, by assuming the date of fertilization, " presumptive ag e of embryo in days " and " duration of fertilizing capacity of sperm ". The segmenting ova enter the uterus at about the sixteen-cell stage under natural conditions, but in Bat No. 76 the ova of approximately thirty-five cells were still in the middle portion of the Fallopian tube. Taking into consideration of the degree of embryonic development for the age of each embryo, it becomes known that the rate of development of the ovum together with the egg transport in the genital tract is delayed in captivity.