﻿GEOGRAPHIC VARIATION. 



9 



than that of the adults and the color darker and duller. The immature 

 skull differs in size and form from that of the adult, but as the sutures 

 disappear at an early age, it is often somewhat difficult to recognize. 



I have found that the best guide to the age of those bats that I have 

 studied is the condition of the finger joints. In specimens young 

 enough to furnish unreliable characters these are always large and 

 loosely formed, with epiphyses separate from the ends of the phalanges 

 and metacarpals, both of which are distinctly enlarged for some dis- 

 tance from the joint (fig. 1 a). In adults the linger joints are small and 

 compact, the epiphy- 

 ses no longer visible, 

 and the i)halanges of 

 essentially the same 

 diameter throughout 

 (fig. 1 b). These dif- 

 ferences are equally 

 apparent in alcoholic 

 si^ecimens and in 

 dried skins. 



GEOGRAPHIC VARIA- 

 TION. 



As compared with 

 other small manmials, 

 bats show remarka- 

 bly little geographic 

 variation in size, pro- 

 portion s, or color. 

 Tlius bleeding indi- 

 viduals of Nycticeius 

 hiimeraJis from Car- 

 lisle, Pa., Dismal 

 Swamp, Virginia, and 

 the extreme southern 

 point of Texas are 

 alike in color,^ while 



in size they agree almost as closely as any three lots of specimens 

 from one locality.^ The only difference that can be found is a slight 

 northward increase in size of the ears. Specimens of Myotis hici- 

 fuf/us from Washington, D. C, are not distinguishable from a series 

 taken on Kadiak Island, Alaska, and skins of Lasiurns cinereus from 

 Minnesota are exactly like others from southern California. While 

 such constancy of characters in wide ranging species is unparalleled 

 among American mammals, the only ones of which it is yet possible to 



^ So far as cau be ascertained from comparison of specimens in alcohol. 

 2 See table of measurements on page 120. 



Fig. 1. 



Wiufcs of Yespertilio serotinus: a, adult: 

 size). 



h. immature (natural 



