262 CALIFORNIA MAMMALS. 



da}'light. Some species spend the day in narrow crevices, into 

 which they crawl, sometimes in large numbers; other species hang 

 from the roof of ca^•es, often in masses; yet others hang in trees 

 from twigs among the foliage. Very little is known about the 

 migTations of bats, but there are veiy good reasons for believing 

 that many species migrate in a method similar to that of birds. 

 Probably few species occuring- in cool climates remain there in 

 winter. 



The number of voung at a birth is commonly one or two; 

 rarely three, so far as is known. With certain species one young 

 may be the rule, with many two is the usual number. iMost have 

 but one pair of mamma;, but others, as Lasiunis, have two pairs. 

 It is probable that some species rear two sets of young annually. 

 Many species are gregarious, but usually the two sexes do not 

 intermingle. 



Suborder Microchiroptera. 



Insectivorous bats of medium or small size; molars with 

 crowns acutely cuspid. 



Family Vespertilionidae. 



Upper incisors small, with a vacant space in their middle; 

 molars with conspicuous W-shaped cusps ; turbinal bones folded ; 

 tail included nearly to tip in the interfemoral membrane; ears 

 medium or large, usually well separated ; tragus well developed ; 

 no distinct nose leaf; hairs surrounded with minute imbricated 

 scales. 



This family of Bats contains seventeen genera and one hun- 

 dred and fifty or more species, most common in temperate cli- 

 mates. The sexes are alike. The young differ but little from 

 ihe adult. There are no seasonal changes of pelage. 



