CHAPTER VI 



SOME REMARKABLE TYPES, AND WHAT THEY TEACH 



So far the creatures which have been discussed have belonged 

 to more or less familiar types, easily met with; being either 

 domesticated or nearly related to domesticated forms. 



In the present chapter it is proposed briefly to describe one 

 or two of the more remarkable modifications of form which 

 certain mammals have undergone, whereby they have either 

 become adapted to live in some environment otherwise unin- 

 habitable, or have adopted, so to speak, unusual methods of 

 locomotion, apparently by the exaggeration of slight structural 

 peculiarities possessed by their ancestors. 



One of the most striking instances of modifications of this 

 kind is happily furnished by one of the commonest of the 

 wild creatures of these islands the bat. Even in large towns 

 such as London, bats are by no means rare in the quieter 

 streets, especially in a neighbourhood where there are many 

 trees. 



The bat is the only mammal which has acquired the power 

 of true flight ; the fore-limbs, as in the case of the birds, having 

 become transformed into wings. But these wings, it should be 

 pointed out, differ fundamentally from those of birds (Fig. n). 

 They are formed, in short, by a delicate fold of skin stretched 

 between enormously elongated and slender supports formed by 

 the bones of the fingers, and extending inwards along the sides of 

 the body so as to include the hind-limbs and tail, as in Fig. 12. So 

 absolutely dependent on their wings have the bats become that 

 they have lost the power of walking. At best they can but 

 shuffle along the ground. The hind-limbs have degenerated, and 

 serve now as supports to the wing, and to this end have become 

 so shifted in position that the knees turn outwards instead of 

 forwards. 



