Summary. In nearly all animals from a laboratory breeding colony that were examined (85/86) the right ovary was significantly larger than the left. Although primordial follicles were present in both ovaries, Graafian follicles and CL were noted only in the right ovary. The left ovary usually had a much less prominent intraovarian vascular supply, and it is suggested that this may play a central role in limiting the ability of follicles to grow on that side. Many of the bats examined very soon after the introduction of stud males had well-developed CL, sometimes of 2–3 different ages, and uteri that had probably been subjected to stimulation by luteal hormones. Such observations made on females that had been housed with a stud male only for 24 h indicate that the black mastiff bat is a spontaneous ovulator with a functional luteal phase. It was common to observe an extended period after the introduction of a stud male during which spermatozoa were present in the vaginal smears from a female almost every day. Most of the ovulations that resulted in pregnancies appear to have occurred during this period. Of the 72 bats with CL, 11 possessed 2 or more CL of the same age, indicating that multiple ovulations can sometimes take place. The right ovaries of all females examined during advanced pregnancy had non-atretic, vesicular or Graafian follicles in addition to the CL of pregnancy.
Keywords: black mastiff bat; ovarian asymmetry; ovulation