CHIROPTERA 33 



partly upon the Horseshoes. It is both the most recent and 

 one of the most complete essays on the subject, and may there- 

 fore be summarised somewhat fully. More exact details will, 

 where known, be found under the heading of each particular 

 species. Meantime, British naturalists have a model life- 

 history with which they can compare their own observations. 



The authors found both sexes of the Mouse-ear living in 

 company in September. The genital organs of the male are 

 then highly developed, but the female organs are small and not 

 remarkable, except that the uterus contains numerous sperma- 

 tozoa. At this time the female is very fat, and remains so till 

 after parturition, whereas the male is very thin. No change 

 was observed in the bats throughout the winter. Towards the 

 middle or end of March hibernation ends and the active life of 

 summer is resumed. Ovulation ensues, and, the ovum having 

 been fertilised, the superfluous spermatozoa are expelled, and 

 gestation commences — almost invariably in the right horn of the 

 uterus.^ A few days usually intervene between resumption of 

 activity and fertilisation, so that gestation commences most fre- 

 quently in the first week of April. After fecundation the females 

 form separate parties, to which no male is admitted, but in which 

 non-breeding females are present. These "nursing colonies," 

 as they may be called, do not break up until the young have 

 been reared, after which they disperse to their winter quarters. 



The date of birth of the young varies a good deal. Thus a 

 female, captured while still hibernating on the 7th March and 

 kept warm, became a mother on the night of the 4th May (fifty- 

 eight days), whereas others taken at later dates brought forth 

 their young between 28th May and 9th June (a minimum of 

 fifty-eight days if they emerged from hibernation on ist April). 

 Apparently, then, the commencement of gestation may be 

 hastened by warmth. Allowing a few days between the termi- 

 nation of hibernation and ovulation, it would appear to last at 

 least forty-nine days, or seven weeks. In many cases its com- 

 mencement is delayed, and females captured on 3rd and 17th 

 April had not yet ovulated, although containing spermatozoa. 



^ Duval, " Etudes sur I'Embryologie des Cheiropteres," in Journ. de fanat. el de 

 la Physiol., xxxi., 93-160, March to April 1895 ; but the authors once found a Serotine 

 with an embryo in the left horn. 



E 



