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NORTH AMERICAN FAUNA. 



the existence of several well-marked geographic races in addition to 

 those now recognizable. 



In the lists of specimens examined it has not been thought necessary 

 to distinguish between those contained in the National Museum proper 

 and those in the collection of the Biological Survey. Specimens from 

 other collections, however, are always specially designated. 



CHANGES IN COLOR OF SPECIMENS PRESERVED IN ALCOHOL. 



Bats which have been kept iu alcohol for a ])eriod of more than a 

 few months become so altered in color that they furnish reliable char- 

 acters of size and form only. The rate and amount of change appear 

 to vary with different species as well as with the strength of the pre- 

 servative fluid and the amount of exposure to light. 1 have seen two 

 lots of specimens of one species collected at the same place and on 

 practically the same date and supposedly treated in the same way, yet 

 after six years' immersion in alcohol those in one bottle still retained 

 essentially their normal color, as proved by comparison with skins col- 

 lected at the same time, while those in another bottle were so bleached 

 as to show scarcely a semblance of their original appearance. 



While the details of the changes produced by alcohol are not known, 

 it may be said that a gradual bleaching and ultimate entire loss of 

 color is the general rule, though as a preliminary step browns are often 

 very noticeably reddened. The subject is one that merits experimental 

 study. 



SEXUAL VARIATION. 



The range of sexual variation in North American Yespertilionicke is 

 always slight and in many cases scarcely appreciable. For the most 

 I)art it consists in the slightly greater average size of the females. 

 Even this is often trifling or absent, as in the case of My ot is lucifugns 

 longicnis from Nicasio, Cal., six males of which average: Total length, 

 95.1; tail vertebriTe, 45.8 ; forearm, 37.8; ear, 11.8; tragus, 7.3; while six 

 females from the same locality average: Total length, 9G.3; tail ver- 

 tebra?, 41.1; forearm, 37.3; ear, 12.1; tragus, 7.2. In general, however, 

 it is necessary to take this factor into consideration when coiupariug 

 specimens from widely separated localities. I know of no instances 

 of constant sexual differences in color among North American Yesper- 

 tUionidcc^ and only one of differences in cutaneous structures, that of 

 Bhogeessa gracilis^ in which the only known male has in each ear a 

 distinct glandular swelling, absent in the two females that I have 

 examined (see PI. I, fig. 7). 



AGE VARIATION. 



Young bats when nearly full grown often present characters different 

 enough from those of the adults to cause confusion in identification. 

 The fur of such immature specimens is usually shorter and more woolly 



