A MONOGRAPH OF THE BATS OF NORTH AMERICA. 



By Harrison Allen, M. D, 



INTRODUCTION. 



The bats constitute tbe order Oliiroptera. Unlike related groups 

 which are equally extensive, the bats do not vary in sufficient degree 

 to be confounded by any possibility with other creatures. By au un- 

 trained observer shrews might be mistaken for mice or voles, some of 

 the smaller marsupials- for minks or weasels, conies for marmots. But 

 the popular impression of a bat is accurate, since this creature is the 

 only mammal adapted for true flight, and no other mammal resembles 

 it. If any mammals exist or have existed that are half bats and half 

 moles, half bats and half lemurs, half bats and half marmots, they are 

 quite unknown to the naturalist. Paleontology is silent as to the 

 origin of the bats, though comparison of their bony framework with 

 those of the Insectivora, Lemuroidea, and Rodentia suggest that they 

 may have arisen from the mammalian stem not far from the points at 

 which the differentiation of these branches began. 



MEMBRANES. 



Let us examine the undissected bat, and endeavor to establish thereby 

 general conceptions of the creature and of some of the signs of the 

 superficies by which its varieties can be named. It is at once seen 

 that the anterior extremities are furnished with greatly eh)ngated 

 fingers, the intervals between which are occupied by two layers of skin. 

 Goldsmith uses a happy phrase when he says "the fingers serve like 

 masts that keep the canvas of a sail spread and regulate its motions." 

 Layers of skin tluis make u}) tlie wing membrane. They are continuous 

 from the last finger and the thumb, or some adjacent surface, to the 

 sides of the body, the neck (both above and below the arm and forearm), 

 and the outer side of the posterior extremity. Each wing membrane 

 reaches below tlie knee and from this point, in varying degrees, to the 

 ankle and tlie foot. The space between the iwsterior extremities is also 

 o<'cn])ied, as a rule, by two adjoined layers of integument which con- 

 stitutes the interfemoral membrane. This structure as opposed to the 



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