AMERICAN BATS — HANDLEY 181 



duce few sperms and because their sex accessories are small, young 

 males (4 to 9 months old) are almost certainly sterile in their first 

 breeding season. 



At times the males, more or less active throughout the winter, ap- 

 proach and probably achieve intromission with lethargic females. 

 The passive state of the females and the absence of a vaginal plug 

 would permit each female to be mated many times in the course of the 

 winter. Since all females in the hibernating quarters contain sperma- 

 tozoa by late October, subsequent copulatory activity on the part of 

 the males must be directed toward females already inseminated. 



It is not known how the male circumvents the female's interfemoral 

 membrane, which during lethargy is usually curled tightly over the 

 abdomen. The only copulation that Pearson, et al., observed took 

 place on a cave ceiling too high to allow observation of detail. How- 

 ever, the male embraced the female from behind in the usual manner 

 of copulating mammals. 



Precopulatory activity was observed among captive bats. The 

 female hung by her feet and was approached from the front by a male. 

 Twittering, the male proceeded to embrace the female with his wings, 

 then vigorously rubbed his snout, perhaps making use of his muzzle 

 glands, over the foreparts and ventral surface of the female. A 

 strong bat odor was noted. 



Sperm storage. — Spermatozoa of bats are viable for surprisingly long 

 periods. In male P. townsendii they retain then- motility for six or 

 more months after they reach the epididymis. However, it is not 

 known whether motile spring spermatozoa are capable of fertilizing. 

 Spermatozoa remained abundant in the uteri of females kept isolated 

 in cool temperatures for as long as 108 days. Probably in P. town- 

 sendii, as in other vespertilionid bats, spermatozoa stored over winter 

 in the female reproductive tract are capable of fertilizing in the spring. 

 After ovulation, spermatozoa disappear quickly from the uterus. 



Ovulation. — In P. townsendii ovulation occurs from February to 

 April. Maturation of the ovarian follicle and its subsequent ovula- 

 tion may depend upon the stimulation of copulation, and this stimulus 

 may be effective even though administered several months before 

 ovulation. It appears that there is an autumnal and early winter 

 period during which ovulation normally wUl not occur. Neither fe- 

 males that are active in winter nor those that are lethargic in winter 

 ovulate before spring, and those that are removed from hibernation 

 and kept at warm temperatures do not ovulate readily. The possi- 

 bilities of sperm storage in the female and insemination of unreceptive 

 females while they are lethargic may have permitted the advanced 

 copulatory period to evolve. 



Gestation. — The duration of gestation may depend upon the body 



