Noone has described in detail the year-round habits and reproductive cycle of a North American bat. The important studies of Guthrie (1933a and b), Guthrie and Jeffers (1938), Reeder (1939), Miller (1939), and Wimsatt (1944a deal with only a part of the reproductive cycles of the species treated, and the almost complete annual cycle of Tadarida cynocephala described by Sherman (1937) is marred by the disappearance of these bats at the critical period of copulation and ovulation. Study of the works cited above reveals that the usual pattern of reproduction of vespertilionid bats in eastern and central North America, as in Europe, is as follows: copulation in the autumn near the time of entering hibernation in caves, storage of sperm by both males and females during long periods of hibernation, and ovulation within a few days of emergence from hibernation in the spring. When brought from hibernation into a warm laboratory early in the spring, females will ovulate within a few days and become pregnant, even when separated from males.It is clear that the most remarkable aspect of bat reproduction-spenn storage and delayed ovulation-is closely related to the phenomenon of hibernation. To us it seemed logical, therefore, to expect different reproductive behavior among bats living in a mild climate in California where long periods of hibernation were not known or expected. What reproductive modifications might be found that would accomodate a light and interrupted winter sleep?The bat chosen for our study was the western lump-nosed bat, Corynorhinus rafinesquei intermedius, This subspecies ranges from southern California north and east into Oregon, Washington, Nevada, and Idaho. Other subspecies are found along the northwest coast and into Canada, south into Mexico and Lower California, and east nearly to the east coast. Except in a few instances noted otherwise, the specimens used in this report are of C. r. intermedius taken in central or northern California, chiefly in Marin, Napa, Lake, and Shasta counties. We have not followed Dalquest (1947) in calling specimens from Marin County C. r. townsendi.We were fortunate in our pursuit of Corynorhinus to capture numerous specimens of each sex in every month of the year. This collection coupled with the important information made available by the banding operations initiated by
