« NOHTII AMERICAN BATS IT. ALLEN. 



Tliis list is scloctod in the main lor couiparisoii in iiienibcrs of a sin- 

 gle family, vi/, the rhyllostoniida'. The last fiyht fbi ins aiv tVon> fami- 

 lies other than the one lirst named. 



It is helieveil that these distinctions may be conveniently inelnded 

 in the characteristic projmrtions of bats. 



In tli^ht the thumb is extended in Ves])eitilioni(he, but partially 

 Hexed in !*hyllostomi(he (exceptiug- Dv.sdkxIus and Piphi/Ua) and in 

 riecoiL 'V\\K' dej^ree of iuelosnre of the thumb in the nuMnb»fane an- 

 swers to the amplitude of the nieud)ranes generally and when extensive 

 tends to ilraw the thumb slightly toward the palm, the space between 

 the tlunnb and index lin{>erbeinj»- moderately occupied by a skin expan- 

 sion. 



rt is a tendency uiuler certain conditions for all jirowth processes to 

 dominate functions other than those which are essential to their own 

 activitii>s. The best i^tMU'ral conception i)\' the nninner of extendiuii' a 

 fold of skin between tlu> limbs is seen in the liatiachia. In the water 

 newts a lon.i>itudinal ridge is often seen extending along the sides of 

 the trunk. This is continuous along the liimler border of the anterior 

 extremity (well (U'veloped in Mvnopoma) and reaches as far as the tip 

 of the lifth <ligit. This fold is sui)plied by the ulnar nerve, which aj)- 

 l)oars to be in its earliest expression a nerve for the skin of the ]>oste- 

 rior border of the forearm, of the tifth digit, and the nuiscles found in 

 these regicuis. The phenomena of a fold of skin extending between the 

 toes is one already familiar, so that the general plan of the skin expanse 

 in a creature so low as the Mvnopoma pretigures that of so highly si»e- 

 eialized a form as the bat without violence and without leaving a single 

 line obscured. Dift'erence of degree and iu)t of kind separates them. 



The very exceptional disposition in the bat for the skin from the 

 trunk to extend the entire lengths t>f the limb, and in the case of the 

 anterior extremity to form euornu)us webs between the produced dig- 

 its, is associated with an inclination for the ears to become greatly ex- 

 panded and for cutaneous otfshoots to appear at the muzzle, chin, and 

 the sides of the face. I^^ven the prepuce is disposed to be redundant. 

 Together with this iiu'lination, dermal structures are highly specialized, 

 so that the sebaceous glands, hair follicles, and tactile btxlies are well 

 deveU)ped. It can be readily surmiseil that special adaptations for a 

 variety of i)nrposes occiijr in thi* group of structures, so that secondary 

 sexual characters are found in the gland nKisses«)f the skin of the neck, 

 and of the skin folds, the tletails in the ears, the pouches of skin, etc., 

 are available for purposes of classitication. 



THE EXTERNAL EAR. 



In this connection h't us ghuu-e at the ])eculiarities of the (^xternal 

 ear. The external ear is markedly nuxlified from the tyi)t> usual in 

 (piadriipeds. Its simplest expression is scimi in the Pteropida- and the 

 Hhinoloi>hida'. In these families the widely sei)arated auricular carti- 



