CHAPTER XVIIl 



MAMMALS OF THE AIR 



CHIEF FEATUEES OF BATS.— The mammals which we now have 

 to consider are not only difficult to observe in their home life — and 

 thus somewhat resemble the beasts under review in the last section — 

 but very peculiar notions exist as to their construction, their life and 

 habits, and the place they occupy in the economy of Nature. Thus, 

 before proceeding to describe a few of the more noteworthy species, 

 it will be as well to pay attention to several general features of interest 

 concerning them. 



These mammals of the air, as we may call them, are either insect 

 or fruit eaters, and day or night fliers. Some of them are both 

 diurnal and nocturnal, for the commonest British species — the 

 Pipistrelle — may often be seen out and about at midday as well as 

 at night. 



The lives of these remarkable creatures are spent either in flight, 

 resting or hibernation, and when we come to examine them we find 

 that they are perfectly adapted to their mode of life and habits. They 

 differ from all other mammals in being able to fly, and hence it 

 comes about that their bodies are constructed in many ways quite 

 differently from those of all the animals already treated of in this 

 book. The Bat possesses a flying membrane which extends between 

 the lengthy fore-limbs and the short hind-limbs, and by means of 

 this and the tail, flijght is made possible. When not in flight this 

 membrane is closed up something like the folds of an umbrella, but 

 when unfolded the animal rests in the air upon a very large surface. 

 This, however, is not sufficient in itself to enable the body to be 

 propelled through the air, and the Bat has to resort to a continuous 

 downward movement of the fore-limbs, "each depression of these 

 limbs bringing in its train a condensation of the atmosphere. The 

 larger the flying membrane, the more easily will the animal be able 

 to support itself in the air, and the more rapidly will it be able to 

 progress. Hence the strikingly large size of the flying membrane." 

 Then again, the bones of the arm act after the manner of the ribs 



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